Soil Organic Carbon: Realities and science for policy advisers and decision-makers

Publication abstract:

On 22 April 2021 (Earth Day), the National Soils Advocate, the Hon Penny Wensley AC, hosted a forum – Soil Organic Carbon: Realities and science for policy advisers and decision-makers – at the National Press Club in Canberra.

The Forum was designed for non-scientists (including parliamentarians, policy officers, advisers and decision-makers) at all levels working on soil related issues and policy. The Forum helped attendees gain a better understanding of the challenges and complexities associated with Soil Organic Carbon (SOC) and its measurement.

Over 145 attendees heard some of Australia's top soil scientists present evidence-based information about SOC to help inform policy advice and decision-making in this field.

Program

Transcript

Mr Peter Wilson, CSIRO: Without further ado then, I would like to introduce The Hon. Penny Wensley, the National Soils Advocate, to deliver the opening address. The former Governor-General, and distinguished Australian diplomat, The Hon. Penny Wensley, has a long-held interest, and substantial experience, in natural resource management, environmental and sustainable development matters, and in Australia's response to national and global challenges in these areas. Penny has held many leadership roles, nationally and internationally. In addition to her knowledge of the environment and environmental policy, she brings to the position of the National Soils Advocate substantial expertise in public policy development, strategy development and implementation, communication and negotiation, and community and stakeholder engagement. Personally, I believe she is indeed a true asset for our Soils. Ms Wensley will provide the opening address, and then facilitate the afternoon. Thank you, Penelope.

The Hon. Penny Wensley AC: Ladies and gentlemen, a very good morning to you all. It's my great pleasure to welcome you to this forum on this beautiful Canberra morning. I do thank everyone who has accepted our invitation and made the effort to be here, and I thank especially those of you who have travelled considerable distances to do so.

As you've just heard, my name is Penny Wensley. Penny is easier than Penelope, folks, so Penny Wensley, and I am the National Soils Advocate. A position that I have held since August last year, so I'm just coming up to my third quarterly report to the Prime Minister, to whom I report directly.

I wear a number of other hats, as a board member of the Lowy Institute, as chairman of the Australian Institute of Marine Science Council, and as chairman of the Reef Advisory Committee, advising the Federal and Queensland Governments on implementation of something called the Reef 2050 Plan, the Long-Term Sustainability Plan for the Great Barrier Reef. And those things all have connections to soils in some ways, but specifically in relation to soils, I have been the National Patron of Soil Science Australia for coming up a decade, and more recently have become Patron of the Soil CRC.

Like others here, I am not a scientist, I am not a soils expert. I am an Arts Graduate. But I do have a background in advocacy. I think it's in my bones and my genes. I was, as you heard, a public servant, a policy officer of the Department of Foreign Affairs and Trade, for 40 years, before stepping down to become Governor, not Governor-General, Governor of my home State of Queensland from 2008 to 2014.

And through those roles, including as Australia's Ambassador for the Environment, addressing national and global environmental and sustainability policy challenges, I really developed a deep interest in those issues of sustainability, and the way in which we, and the rest of the world, manage the vital systems that sustain life on Earth.

I also developed a special interest in the nexus between good public policy and science. And that's what lies at the heart of this forum, hosted by my office. The office of the National Soils Advocate is quite small. It sits within the Department of Prime Minister and Cabinet. And with just our little small team, we decided that we need to be strategic and selective about where we invest our effort, and look for ways where we can make a difference, where we can add value. Where we can contribute to, and facilitate, productive discussion on issues of national importance relating to soil. And the subject of soil carbon seemed an absolutely obvious choice for this, our first forum.

Twenty or 30 years ago, interest in soil carbon was held almost exclusively by farmers, and by the researchers and the agronomists, like Sue, that supported them. This interest was driven, again very obviously, by the link between soil carbon and soil health. Soils with higher soil organic carbon are more biologically active and healthy. But now, now this interest, somebody used the word a couple of minutes ago, has really accelerated. It has expanded far beyond farmers, to include parliamentarians, and we now have a Parliamentary Friends of Soil group, and we've been steadily talking to them about these issues. Includes policy officers in government departments, many of whom are here today, policy advisors, decision makers. A really broad range of people who are not scientists.

And it's unlikely to escape the attention of many in this room, that soils have been elevated, by the Prime Minister, to a matter of national importance. Discussing soil health at two Bush Summit speeches, and I think there's another one coming up fairly soon, but these were in 2019, when he announced the appointment, the development of a National Soil Strategy, and also the establishment of a permanent position of a National Soils Advocate, and then again in 2020, when he announced my appointment to the position. And right here, in the National Press Club, in February this year, when he was setting out the Government's priorities for the coming year, he talked about the National Soil Strategy. He said it will include practical actions, and focus on the development of a national monitoring program to assess the condition of Australian soils research and development, and to assist with implementation, capacity building and extension. He added also, it will be a fitting legacy to the great work and advocacy of our former Governor-General, and first National Soils Advocate, the late Major General Michael Jeffery.

As the world looks for solutions to climate change, interest in soil carbon as a potential element of the solutions has been growing. And as we are here, I believe the Prime Minister is presenting Australia's position at President Biden's Leaders' Summit on Climate, to galvanise efforts by the major economies to tackle the climate crisis in preparation for the UN Climate Change Conference COP26.

I was our principal negotiator on the UN Framework Convention on Climate Change for five years, and I attended COP1, which shows you how long I've been thinking about these issues. COP1 and COP26, that's a long difference. I also think it's good that we're not the only ones who have chosen to host an event on Earth Day. But it was such a beautiful fit for us dealing with soils.

With this growing interest in the subject, nationally and internationally, we thought it would be both timely and useful in a practical way to hold this forum, focussing on the policy science interface. With so many policymakers and advisors and not a bad number of scientists in the room, this might seem to be something of a statement of the obvious, but as the lead-in to today's presentation discussions, I really want to emphasise the following.

Through a process of discovery, scientists need to present evidence-based information that has a high degree of certainty, and policymakers need to design policy that is underpinned by science to create realistic and achievable impact on the way we go about our business. Hence the word realities. And I want to share with you, and some of you will be familiar with this maybe, some thinking from Professor Ian Chubb, former Australian Chief Scientist. Ian and I work very, very closely together on reef issues and reef science. We both of us chair one of the two advisory bodies advising the Governments. Ian has said some really good things on this subject. All scientists must cope with the political realities of helping to translate scientific evidence, replete with uncertainties, into clear‑cut laws and regulations. Because of this, many say, science can underpin good policy, but it rarely defines it. Policymakers need scientific evidence to guide decisions. The mission of modern science is not only to create new knowledge, but to use scientific knowledge to address social issues.

The way in which science comes into policy, is often almost inevitably incremental. There can be something that, a catalysing event, that will stimulate policymakers' appetite for scientific evidence, and we've seen it in abundance with the pandemic. But in our case, it's the heightened interest in soil carbon's role in climate change mitigation that has really given this a kick along.

Looking now at what do we mean by good or real science? Ian Chubb describes science as the following. Scientists unpick, they examine. They reconstruct. They seek to replicate, to reanalyse and reinterpret. And when they do, certain directions and conclusions that withstand this scrutiny, become much more central to our thinking. When an observation has been made and confirmed many times, it can be considered secure, if not absolutely certain. If different evidence comes to light, and it withstands the scrutiny, it will eventually shift the way we think.

The scientific community works on evidence and facts. Ultimately, decisions and policy need to be made on the weight of evidence, sometimes called a scientific consensus. And Ian said, I am encouraging you to use science, I am encouraging you to use the right science. It wouldn't be good to have an idea in mind and then go and find one scientist to support it, then use that as evidence for your decision. Where there is a majority view in science, that's what you need to listen to. That's what we need to build on when we develop public policy.

It's our aim to have in this room, and I think we've achieved it, a real cross section of people who are working in science, in policy, in advisory roles. We wanted to facilitate that conversation and that engagement, and we wanted to deliver science from those who are really among Australia's leading experts, to you in a way that makes sense to you as those policymakers and decision makers.

We really hope that you get something out of today's forum, that you do find it timely. That it will assist you to build some new networks and connections. Please don't just talk to the people you know. Please make sure that you meet some of the speakers, some of the presenters, and so that we can follow up these conversations beyond this.

You are truly going to hear some of Australia's top soil scientists present that evidence-based information about soil carbon, to help inform policy advice and decision making in this field. Gaining a better understanding of how soil carbon works, and I am certainly hungry and thirsty to swallow up some of the facts and figures that are going to be presented today. Gaining a better understanding of the challenges and the complexities associated with soil carbon and its measurement will be very useful. I have been concerned that as the debate has picked up and picked up, and there has been more and more discussion, that there has been perhaps some oversimplifying of things. There is a view that there are some magic solutions out there. There's no silver bullet, but maybe, maybe, we can find our way towards a better understanding of those complexities, of those realities, and help this country move forward to making some good sensible achievable decisions, and good policy underpinned by good science in relation to soil carbon.

Thank you all for being here.

Transcript

Mr Peter Wilson: Our first speaker this morning, is out there somewhere, Dr Liz Clarke, CEO, Soils for Life, there she is. Dr Clarke has worked as a practice-driven researcher, educator, policy advisor and mentor for the non-profit and private sector across three levels of Australian Government and with the community and volunteer groups. She has led teams and organisations in Australia and internationally, as well as being CEO of Soils for Life. Liz currently holds visiting fellowships at ANU Fenner School of Environment and Society and the Institute for Land and Water and Society at Charles Sturt University. She holds a PhD in human ecology from ANU. Liz will discuss landscape functions, provide an overview of the complexity and diversity of soils and landscapes and the ecological processes that underpin soil carbon. Thank you, Liz.

Dr Liz Clarke: Thank you, Peter and thank you, Penny for the introduction. Good morning everyone. As Peter mentioned, I'm not a soil scientist. I'm an agricultural scientist who went back and did a human ecology PhD because I felt that the thing that was missing in agricultural space was a better understanding of people, decision-making and complex systems. So, some of my colleagues, my agronomic colleagues at the time, said, when I went back to do my PhD, "Ooh you're embracing the dark arts of social science".

I'd like to talk a little bit today, as Peter mentioned, about the broader context that we're talking about with soil carbon. Let me just find my clicker. Penny talked about the broad ecosystem of people and organisations who are involved in the soil carbon space, and she talked about the science policy interface. I'd like to just add a third leg to that stool, which is the practitioners. These are the ones at the coalface. These are the ones who are going to make the action happen. So, in my context these are the farmers, the agricultural land managers and land managers of all types and descriptions. I'd like to focus a little bit on that and the complex context in which they are operating.

This is a slide from the Global Soil Partnership, which I think is a nice description of all the things we need to think about in terms of soils and mitigating climate. But I think we also need to keep in mind the high-level vision that we're focusing for. We've got a number of challenges that we're dealing with at the moment, including a pandemic, climate change, biodiversity collapse, economic issues, equity and so on. And I'd just like to briefly say that our organisation, Soils for Life, which was actually founded by the previous, or the very first soil advocate, Michael Jeffery, is very much focused on supporting agricultural land managers to regenerate soils and landscapes. So, this is our business, and of course, we work very closely with the Soil Advocates Office.

I'd just like to show you this slide just to show that healthy soils underpin all of the SDGs. If we are to achieve the SDGs, we absolutely need healthy soil and that's not just because I'm obsessed with soils, it's a reality. But also, to focus in a little bit on soil organic carbon, there's probably four of the SDGs that are really critical. The first one that we focus on a lot is climate change, climate action, is taking carbon out of the atmosphere and putting it back in the soil. But there's also zero hunger. Food security relies on us managing our soils well, including sequestering soil carbon.

The next one is clean water and sanitation. Clean water and sanitation – soil is our best mass water storage device in the landscape and we forget that. We forget the importance of storing water in soil and that if you have more soil carbon, if you have better structure, you're going to be able to store more water.

And lastly, soil underpins terrestrial life. Without soil, we can't have that terrestrial biodiversity. And that's just a quick graphic just to show you some of the challenges we're dealing with at the moment which are relative, really quite complex. Use that hand sanitiser, but just remember that there's a few waves coming behind.

Okay, so now I've done the global thing, let's get back down to the local level and talk about that third leg of the stool which is the practitioners, and in this case, in our case, at Soils for Life we're focused on farmers and agricultural land managers. Decision-making and action happens at the farm-scale, and there's three things to keep in mind about that. Firstly, that agricultural landscapes are complex social ecological systems, not just ecological systems but social ecological systems. And the second thing is that producer decision-making is absolutely fundamental. Policy success needs to support and enable locally adapted decision-making. What does this look like? What is it that keeps our farmers and agricultural land managers up at night, in the challenge of making decisions in these complex self-organising systems, and I'll explain what I mean by that shortly?

The first thing is profitability. It all stops if it's not profitable. If we don't have profitable farms and profitable farmers, if they cannot sustain a livelihood, we can forget about all of the other things that come with it. And that's absolutely crucial. You need farmers three times a day. You need a doctor maybe once every month or maybe less often if you're very healthy, but you need a farmer every single day, three times a day.

The second thing, I would say that all farmers are interested in sustainability, from an economic, ecological and a social perspective and I'd just like to give you a quick statistic, FAO reports that erosion carries away 25 to 40 billion tonnes of topsoil every year globally. If this continues, and we don't take action, by 2050 we will have lost 1.5 million square kilometres of arable land by 2050. That's basically all the arable land in India, just to give you a bit of a perspective.

Finally, and most importantly, farmers are risk managers. This is what they do every single day. They manage risk and they try to make their systems more resilient. And this includes drought resilience, flood, fire. I mean we're very much aware of the impact of the recent fires, not just on urban communities but on farming communities. And soil carbon's a really important part of this risk management. I'm just going to give you complex self-organising systems 101. For some of you, this is teaching you to suck eggs, but I think it's worth going through.

Very simply, we talk about systems as three basic types; simple, complicated and complex. Simple systems are, you could use as examples, many of our technological innovations. Things like making a telephone, making a mobile phone or a radio or a car or a plane and that relies on classical mechanics and thermodynamics. There's not too much ambiguity and uncertainty there.

When you move up to complicated, things like the motion of gasses in a jar, if you've done physics or chemistry, growth of the universe, an airport. An airport is complicated, it's not complex. It can be managed; it can be organised; and a mass transit system.

But then you come to complex, and these are self-organising systems. These are systems in which you can't predict. You can monitor but you can't predict. And this includes landscape management, soil organic carbon, food security, climate change action, maintaining biodiversity and also the weather. So, these ecological systems have certain characteristics. The interrelationships are key. They're more important than the things. They have feedback loops. They have emergence. They're non-linear, so they're less predictive, causality is hard to establish and they're self-organising. I just threw this in quickly, just to show you, this is a classic example that's used in complex science which is birds flocking. So, birds don't set out with a flight plan tucked under their wing. They respond to the birds either side of them, to their neighbours. So, they keep a certain distance from them and they fly adaptively. They adapt and respond to the environment around them. So, if a hawk flies through there, that formation's going to suddenly change.

Now I come down to the nitty gritty of it. Agricultural landscape function, which is what I'm talking about today. Now this diagram is really a very, very simple, highly simplified picture of the complexity of landscape management including soils. I tend not to separate landscapes and soils. They're all very interlinked. This diagram is a nice, simple heuristic that we use in our work in working with farmers and other stakeholders because it's a simple way of being able to talk about these processes without getting too far down in the weeds. Though that can be necessary as well. It's kind of like a prism in which you can view different aspects of the system, and in this case today we're talking about soil organic carbon.

I'll just very quickly go through each of those five functions, if you like. The human social cycle, this is one that gets overlooked constantly, and this is very much going back to the ecosystem that Penny was talking about of that interface between policy, research and practice. And then you've got consumers, and you've got value chains and you've got supply chains and then you've got the farm businesses themselves which involve a lot of complex decision making and they're not just rational economic decision making, these are families, these are livelihoods. So, this is a really important one to consider. And from my previous experience, I've spent most of my career working with farming communities and I think we can generally rely on farmers to be innovative, to use adaptive responses and to use iterative approaches to management which is really about managing in a complex system. This is a really important tool and perspective to remember when we're setting policy around these things.

The second one is dynamic ecosystem communities. Here we are talking about the composition of communities and the interrelationship between them. We are actually talking about collaboration rather than competition. So, this diagram shows a diversity of communities both above and below ground, and other speakers will talk in more detail about this, this is just the high-level overview. But all of those elements interact to make up the ecosystem, and how they interact is really critical. So that can be a positive collaborative or it can be a negative competitive. For example, in a positive case, a soil ecosystem can actually supress a pathogen. Having a healthy biodiverse system with positive interactions can supress a pathogen, and I won't go into the science of that. And emergence, that characteristic of complex systems comes out of these positive and negative interactions, and this is a way in which the system state can shift. I won't go into too much more of that. The soil mineral cycle is also really critical. So, while we're talking about soil carbon here, soil carbon has a huge influence on the nutrient cycle, on how we store and use cycle nutrients in the soil. So, as you know, there's a whole lot of nutrients that plants need to survive, NPK, sulphur, a whole lot of micronutrients and so on. So, all of these organisms, the soil micro-organisms, the plants and the organic matter, play a really critical role in managing those mineral cycles.

Water is really critical. I hear a lot of commentary about how you can't store soil carbon if you don't have water in the system. Well, you can't store water in the system if you don't have soil carbon. So, it's kind of – it works both ways. But one of the things about having a biodiverse system with good vegetation cover, is that you actually improve the ability of the soil to take in and hold more water and the more soil organic carbon you have, the greater your water holding capacity. And I'm really generalising here. There's a lot of nuance in there, but I'm just generalising for the sake of this presentation.

Last, but not least, there's the plant. There's the solar energy cycle. Right front and centre there is plant which is our very best, most sophisticated piece of technology we have for soil carbon storage. We cannot equal this piece of technology. We can't reinvent it. It is a brilliant thing. It is a photovoltaic cell which little machines inside it called chloroplast which capture carbon from the atmosphere, energy from the sun and turn that into sugars which is the building blocks of everything, of all, soil carbon, life, organic beings, et cetera.

I'm just going to flash this next slide up really quickly because there really isn't time to talk about it in detail, but this comes from some of my work with working with complex systems and it's based on a paper, a very famous paper by Donella Meadows who was one of the – the Club of Rome who did the limits to growth, and this is a really critical understanding of how systems work and how we leverage systems, how we leverage change in systems and that the deepest leverage is the hardest to get at and the least visible, and the shallowest leverage is the most visible and the easiest to get to. So when you're looking at transforming systems, which is essentially what the people in this room are trying to do, you need to think about both deep and shallow leverage. But I think you'll get the materials afterwards so I'll give you a chance, I'll let you study that at your leisure.

We come to the final slide. I'd like to leave you with four key messages. Firstly, we need all available solutions to put carbon back in the soil. Penny referred to this, there's no one single silver bullet. We're going to need multiple approaches, multiple people doing multiple things to make this work. and we also need to keep in mind the bigger picture of why we're doing this and what else this feeds into.

Secondly, soil organic carbon is both a mitigation and an adaptation approach. It plays a crucial role in building resilient, productive landscapes. It's also important in terms of drought resilience, in terms of making landscapes more resistant and resilient to fire, which we're going to see more of in the future. And the third point is that the perfect is the enemy of the good. I think we need to avoid focusing excessively on precision in quantifying and predicting rates of sequestration when every tonne of carbon counts. Every tonne of carbon counts. And we also need to remember that uncertainty and risk are inherent in complex systems. And I think this is extremely important in the policy space because those of you who are doing policy advice, you're dealing with extreme complexity, the possibility of perverse outcomes and all of these things are highly relevant and salient.

The last point is that land managers will be the decision makers and they will carry much of the risk. And we need to remember that, we need to remember that they have serious skin in the game in this process, this is their livelihoods. And I think the system's thinking perspective, for most of them I think, is second nature. Nothing exists in isolation, everything is interlinked. And also, that soil organic carbon isn't the only game. It's a really important game, but all of the other elements that go into landscape management, must also be considered and will contribute to soil carbon storage.

Also economic incentives, they're a key part of enabling producers. But it's also about making these processes accessible to producers. For example, we're working with a group down in the Albury Holbrook area who are very successful farmers who are regenerating their landscape. They're having great outcomes in terms of soil organic carbon, but they're struggling to access programs to gain benefits from the work that they're doing which is a societal good.

Keeping it simple. Producers are innovating, so we need to focus on outcomes rather than prescriptive process, and this comes back to the complexity thing. So, it's really the outcomes that matter.

And the last point is that monitoring and validation is expensive. So, we need to enable funding for collaborative farm-based research and lower cost monitoring. That connection between research policy and the farm-based activity, that needs to inform the research and the policy and that's absolutely crucial if we're to succeed in this space.

That pretty much wraps up my presentation. Thank you all very much for your attention, and I'm very much looking forward to the rest of the presentations today.

Summary: Parts 1B and 1C: The science behind SOC

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Associate Professor Frances Hoyle, SoilsWest, The University of Western Australia; and Professor Daniel Murphy, UWA School of Agriculture and Environment, The University of Western Australia.

What is SOC?

Soil organic carbon (SOC) is a measurable component of soil organic matter. It is made up of living organic matter (such as microorganisms, animal wastes and dead and decaying matter), which is primarily carbon (~ 45%), but also contains hydrogen, phosphorus, sulphur, potassium, calcium and magnesium. Soil organic matter is approximately 58% carbon. Soil is a complex matrix of minerals, pores, organic matter and soil organisms that is both a 'sink' and 'source' for greenhouse gas emissions.

What is its function in the soil, linkages to soil health?

Microorganisms digest up to 90 percent of the organic carbon that enters a soil in organic residues. In doing so, they respire most of this carbon back into the atmosphere as carbon dioxide. While up to 30 percent of organic inputs can eventually be converted to soil organic matter, depending on soil type and climate, in Australian agricultural soils this value is often significantly less - with the majority of this present within the particulate (bioavailable) fraction.

Soil organic matter underpins soil function in terms of supporting soil biological processes (e.g. energy source for microbes, nutrient turnover, and below ground biodiversity), soil chemistry (e.g. buffers pH, binding heavy metals, cation exchange capacity, and degradation of contaminants) and the physical structure of soil (e.g. improving soil structure, water holding capacity and buffering against temperature extremes).

Impacts on SOC content

Changes in stable SOC generally occur very slowly (over decades), and it is often hard to measure small changes against a relatively large background of soil carbon. Changes in SOC are largely determined by how much biomass is grown and retained above and below ground.

There are 3 main factors influencing the ability of a given soil type to retain SOC, these are:

Soil type - Naturally occurring clay in soil binds to organic matter, which helps to protect it from being broken down or limits access to it by microbes and other organisms. Increasing levels of soil acidity are linked to low carbon use efficiency in microorganisms, influencing the accumulation and decomposition of SOC.
Climate - In comparable farming systems with similar soil type and management, soil organic matter increases with rainfall. This is because increasing rainfall supports greater plant growth, which results in more organic matter accumulating in the soil. As the climate gets hotter and drier, organic matters build up can be limited due to productivity constraints and accelerated decomposition rates. Where soil moisture is available in warm to hot environments, decomposition occurs more rapidly.
Management practices – land and soil management practices can both positively and negatively impact of SOC levels. For example, maximising crop and pasture biomass via better water-use efficiency and agronomic management can increase organic matter inputs where sufficient inputs are retained. However, frequent large inputs of organic matter are required to increase SOC. It is possible in cropping systems that 'improved' management practices where measured through time, reflect a slower rate of loss rather than accumulation.

What is the probability of successfully increasing SOC?

The probability of successfully increasing SOC is low where net primary production (i.e. plant growth) is limited and in sandy soils. The opportunities increase significantly in cooler, higher rainfall climates (but only if the soil is not already at capacity) where waterlogging is not a factor, and at depth – where the subsoils are not close to storage capacity. The likelihood of building SOC is dependent on the balance of inputs (i.e. organic residues) being greater than the losses recognising background biological turnover of organic matter (2-4% annually), as well as any losses associated with extreme events or management induced changes.

Transcript

Mr Peter Wilson: Our next speaker, Associate Professor Fran Hoyle from SoilsWest and the University of Western Australia. Fran has extensive experience in fundamental and applied scientific research and is active in research and communication in soil biology and organic matter management. Thank you, Fran.

A/Prof Frances Hoyle: Thanks Pete. All right, morning everyone. So, we're going to transition in and talk a little bit about soil organic carbon and what it is. And just to start that off, I've just put up a little advertorial for some of our soil quality e-books. So, these are a free resource to download from Apple Books. The third of these in the series is actually on managing soil organic matter in farming systems, so please have a look and consider whether they're useful to you. This is the first five in a series of 10 that are supported by funding through GRDC.

If we think about soil carbon, we are really talking about soil organic matter with carbon being a component of that soil organic matter and when we talk about carbon function in soils, it is really coming back to the premise of talking around soil organic matter function in soils, so carbon is an integral component of that. Soil organic matter obviously has its origins in living plants, animals, their by-products and the microorganisms that are associated with our soils. That organic matter is primarily carbon, so 45 per cent carbon in organic matter, but it also contains hydrogen, phosphorous, sulphur, potassium, calcium and magnesium.

Soil organic matter as it decays obviously loses some of the nutrients associated with that organic matter and so we get an enrichment of the carbon that comes into that soil organic matter pool. It includes the living in terms of our microorganisms and some of our living roots but it also includes the dead and decaying materials less than two millimetres in fractions. So, when we talk about soil organic carbon, it is generally analysed from a soil which has gone through a sieve of two-millimetre aperture and then the carbon is our concentration within that organic matter.

It is a complexity when we start talking about soils and soil organic matter function in that it's a matrix of the minerals, the pores, the organic matter, the organisms that live within soil and when we talk about organic matter, we need to recognise that it is a very small pool of what is a very complex matrix. But that very small pool is integral to the functions that are important to production systems, so the nutrient supply, the water cycling dynamics, the biological fertility in terms of what's driving our microorganisms.

Total organic carbon is the measure of the carbon derived from that organic material. It differs from the total carbon, which measures all carbon in soil, so that includes the carbonates, such as lime, for example. The age and composition of soil organic carbon is very different; it varies from very recent carbon inputs such as root exudates, to carbon that is thousands of years old, so indicative of indigenous management of the lands, a lot of is char material that is resistant. But it can be separated into fractions and a lot of the research looks at the fractions of carbon to see where the changes are happening. Most of the changes would be measured in that bioavailable labile pool.

The picture depicts on the left the particulate organic matter, which is that organic matter which is labile, it turns over very rapidly, it's the food or energy source for microorganisms and it is what drives a lot of the functionality associated with full organic matter. Then we have our mineral-associated organic matter which is our humus and our resistant organic carbon pools and that cycles very slowly. Our humus pool is quite stable, it turns over in decades. Whereas our particulate organic carbon pool may turn over in hours or days or up to a year. Our resistant organic carbon, which is the very stable carbon pool, is actually in place for thousands of years. So, our particulate carbon pool is the one that our growers are managing year on year and having an influence on. Our humus pool is the pool where they are changing within their lifetime and within their children's lifetimes. But the resistant organic carbon pool will be the basis for ongoing, where we see very little change.

We can see that particulate organic carbon pool, which is made up of parts of leaves, root exudates, living organisms, it's very bioavailable. The humus pool, again which is microscopic, is by-products of organisms and the compounds of those and it sticks to soil particles in terms of being able to be protected from degradation. A lot of the more stable pools are the pools where they have a mineral association, so they're linked to the soil or they're within aggregates in the soil, so they're protected from decomposition.

Then we have that stable char dominated material and it's not the type of char that is necessarily visible to the eye, but that can make up between 25 and 30 per cent of the organic carbon in soils. When we talk about a pool of organic carbon, you might think, well a third of it is very resistant, it's not going to change over thousands of years, then a third of it may be in that particulate bioavailable pool, so that's the pool driving your systems and then between 40 and 60 per cent in the humus pool.

Liz showed this image, but it was just to reiterate that carbon is fixed from the atmosphere, so we get our organic matter into soils in farming systems primarily through plant biomass accumulation, so the accumulation of pastures, crops, feed sources that are then using that light energy to convert carbon dioxide, water and nutrients into organic matter.

Carbon inputs to soil include primarily in farming systems the plant residues that are retained within the system, recognising that we are taking offputs from the paddock, so the plant residues that retain the roots that are protected within the deeper layers of soils, root exudates and the microorganisms, as well as our animal wastes. We do have a carbon export through produce in terms of we take off grain, milk, meat, all sorts of products which reduces those inputs back to the soil, so you've got your inputs and your outputs. And we can have off-paddock sources of carbon, so this is where you talk about composts or biochars or other organic compounds that are brought into paddocks from off-paddock and can be contributing to the soil organic matter pool and that is where we start to talk about viability and function of those products within the soil.

One of the other things that we need to keep in mind is we don't just talk about carbon losses in terms of the new residues that we put in. If we think about a soil organic matter bank, it is just that, it is a bank. It's a little bit like a savings account where you are putting in little amounts of money and you are then taking out amounts of money in terms of achieving the goals within your business or within your personal life. We have a background turnover in the soil organic matter bank of between two and four per cent per year. That is happening continually throughout the year and doesn't stop.

So, we have a soil organic matter bank turnover and then we have our new inputs going into the system. Our new inputs are the residues, the root exudates and between 50 and 90 per cent of those organic matter inputs or carbon inputs are often respired as carbon dioxide. If we think about the carbon that goes into systems in terms of putting into our bank, our microorganisms are busy utilising the bank to provide nutrients, to provide biological function, to provide disease suppression and resilience in those cropping systems and so we withdraw from the bank, I guess, if you like, in terms of the amount of carbon that we keep in, whereas we're using some of it to perform the functions that we need.

Then we have extreme events such as erosion where, as previous speakers have mentioned, we lose a significant amount of our surface within a wind or water erosion event and if you think about where organic carbon is profiled in soil, it is predominantly in that surface soil, the top 10 centimetres. So 60 per cent of our carbon, for example, from zero to 30 centimetres, would be in that top surface layer. If we lose a component of that layer, we are losing a significant proportion of the carbon associated with that, as well as our biological fertility.

How much carbon enters the soil? This is really just a rough, back-of-the-hand guide as to what we can expect. We are talking about a carbon baseline where we've got a paddock which has a carbon concentration of 1.2 per cent, it has a bulk density of 1.5 and we're talking about the top 10 centimetres' depth. We calculated out that soil to 10 centimetres holds 18 tonnes of carbon per hectare. We've talked about the inputs, so we're cropping this soil, we've got a wheat crop on it and we know our harvest index is 0.45, so our crop is yielding 2.5 tonnes on average over the last 10 years. If we use the harvest index, that's equivalent to 5.6 tonnes of biomass above ground.

We're then taking our yield away, so we've taken two tonnes of biomass away, so we've got 3.6 tonnes of biomass left, but we know that there's biomass below ground as well, so we need to attribute the fact that we have below-ground biomass and in a cropping system, quite often that's about half of what we see above ground. I've used that ratio here to calculate out 5.4 tonnes of biomass. We've got some root exudates, organic matter is 45 per cent carbon, so with that 2.5 tonne yielding crop, we have 2.6 tonnes of carbon per hectare going into the system.

We then have our organic matter bank turnover. We've got 18 tonnes of carbon, we lose three per cent, so I took the middle ground and that's equivalent to 0.454 tonnes of carbon per hectare per year. The decomposition of the new inputs, where we've got a carbon use efficiency of just 25 per cent, we're losing two tonnes of carbon per hectare of the new inputs. The carbon balance, in a paddock that's yielding 2.5 tonnes per hectare, there is no measurable change, if you looked at that through time.

You've got to then contemplate how you relate that to other environments. Drier environments perhaps which are lower yielding are potentially going backwards. Higher yielding environments which have high levels of inputs, potentially slowly are accumulating carbon. But it is why it is such a challenge to build carbon, it's not impossible, it's a challenge, in that we have this continual turnover as well as our microbes are using that carbon as an energy source to perform their function. They're like us, they need food.

How is it linked to soil health? We're talking here about soil organic matter again, recognising carbon is a component of that. We know it's an energy source for microbes, supplies nutrients, stores them, provides resilience in terms of an ability for a soil to recover from a stress. Lots of biodiversity below ground and obviously an ability to suppress diseases and pathogens. Buffers pH, so it has a chemical function as well as a physical function.

And part of the reason why we're here, it is both the sink and the source of carbon and it is carbon sink when the amount of carbon dioxide taken up by that soil is greater than the amount that is released and it is a carbon source when the uptake is smaller than the amount of carbon dioxide that is released. Whilst we're talking about carbon often in the context of a carbon sequestration, we can't forget the functionality around soil organic matter and that component of carbon that is associated with it. That is a key driver for why our growers would consider.

If we think about function, it's also not so simple. If we think about the fact that we have a range of different soil types, we know, for instance, that as you change your soils and increase the clay content, the influence of organic matter in those soil changes. In a sandy soil organic matter is extremely important for things like cation exchange capacity or water-holding capacity. In all soils it's important for biological energy. As we move into heavier clayed soils with a greater proportion of clay, that clay takes up the role of providing the cation exchange. Organic matter functions in very different ways in different soils and we can put some value around that.

We talked about water-holding capacity before in organic matter and yes, organic matter stores a great deal of water. However, you are also looking at organic matter in the context of a soil matrix, so it is maybe 1.5 per cent of the whole of the soil. If you thought about what that value was, for each percentage increase in soil organic carbon, so moving from one per cent soil organic carbon to two per cent soil organic carbon, we'd get between two and five millimetres of water being held, that is additive above what our soil would otherwise hold.

That can be really important. It doesn't sound like a lot sometimes, but if for example, you had five millimetres available to you five times a year, so you had 25 millimetres and you know that each of those millimetres is 30 kilograms of grain, you've got half a tonne of grain there. That is better yielding than you had previously, so it is of value.

This is a trial where we've had 100 tonnes of organic matter added to the paddock over 12 years, so 100 tonnes. After 13 years, we've doubled the amount of organic carbon in the system, so that's terrific, we've managed to accumulate carbon in it. But we also have a value from the potassium, the nitrogen, water-holding capacity, there are multiple functions and values to the soil organic matter change that has happened in that system. You can see a visual there on the right-hand side where just a change in potassium can influence the amount of crop biomass growth and crop yield within those systems, so they are important aspects of the function of soil organic matter.

Again, if we think about the fractions of organic matter and what they contribute to these different functions, they will also have different influences. For cation exchange capacity, it's largely dependent on the humus and the resistant organic carbon pools. For our biological processes, it's largely the particulate organic carbon or that labile carbon and the humus pool. We know that the carbon fractions vary in the influence on soil and we know that the particulate organic carbon pool is more responsive to management, with those changes most evident in the surface soil.

If we looked at some long-term work, many of the changes that are measured in the soil organic carbon pool are in that labile pool. This is an example from Merredin, which is a dry land environment in Western Australia, it's low rainfall, probably yielding about 1.2 tonnes of wheat per hectare. After 30 years in this particular example, with stubble retain versus stubble burnt, we have the same amount of organic carbon in that system, so it has not changed.

Now part of the reason is because when you burn stubbles, you're obviously having a flush of carbon dioxide immediately and we lose that carbon. If we think about long-term fate of organic matter going into the systems and its decomposition and the fact that we're decomposing most of it, the long-term carbon dioxide flush from that material is quite similar. However, it doesn't tell us how well that system is functioning.

In this particular example, we have a particular organic carbon pool that is 30 per cent higher where we've retained our stubbles. It's the food for the microorganisms that are in the soil, it's the nutrient supply pathway for that soil, it is the part of that soil that is able to supply a bit more moisture for a bit longer to keep that crop going and in this particular example, it was the equivalent of about 50 kilograms of nitrogen per hectare, so there is a known value. If we then associate that with our biological fertility, our microbial biomass, so the mass of organisms in the soil, it's 50 pe cent higher. So we know this system is more biologically active. So sometimes it's quite dangerous to talk about soil organic carbon without the context of what those pools and biological pools are doing.

Again, a dataset from WA, but it's a multiple number of paddocks across the state and this just shows you that many farms have very different values for soil organic carbon. On the bottom we're looking at total carbon in terms of tonnes of carbon per hectare. If we had one per cent carbon to 10 centimetres depth, with a bulk density of one, then you have 10 tonnes of carbon. But this is just showing you two farms on each end of that red line, where one farmer has 10 tonnes of carbon but only five per cent of that carbon is active, or labile and another farmer where 50 per cent of the carbon is active or labile. Now neither of those things is bad.

This example at the top might mean that this grower has prioritised high nutrient turnover in his systems. He's not degrading his soils, he's got the same amount of carbon, but he's got high nutrient turnover. This grower has a more stable or slower carbon turnover, so they may, for instance, be in a situation where they are more confident of maintaining that carbon long term in a marketplace.

If we look at what impacts soil carbon, this is a depiction by Ingram & Fernandez and we look at the defining factors for what attainable level of carbon can we achieve in different soils. The first defining factor is around soil factors, so soil type, the amount of clay, the bulk density, the mineralogy of the soil. There's very little that we can do as land managers to influence that.

The next limiting factor is climate. If you think about climate, rainfall and temperature, it drives both your inputs because it is driving plant biomass accumulation, you need rainfall and you need temperatures suitable for a plant to grow, but it is also driving your decomposition. We know that with increasing rainfall we can degrade carbon for a longer period of time and with each 10 degree increase in temperature, we double the rate of decomposition. So, we know that it drives the losses.

Then our decreasing factors or our potential to increase, if you like to make it the other way, is the way that we manage those soils, so can we avoid erosion, can we have plant types that are grown for longer periods of time in the year, can we increase the diversity of our rotations. All of those things are optimising management to reach that attainable level of carbon. And we of course can add external carbon.

I wanted to depict to you the influence of the soil type and climate. This is a one site, 10-hectare paddock, it naturally ranges in clay content from less than five per cent to 45 per cent. You can see on the graph on the left that as clay content increases, the soil organic carbon has increased, so it's had the same management, it's under the same climate, it is the same paddock. We know that soil type is linked to the amount of carbon that we can accumulate. If we then look at the graph on the right, which looks at the amount of particular organic carbon or humus, we also know that those soils with high clay content have a higher concentration of that more stable humus pool.

We know a natural equilibrium exists for the retention and loss of organic matter, but we know there's also significant seasonal variability. In a low cation soil, a lower proportion of organic inputs are protected and maintained and this is a really critical point in some of those soils that are very sandy. We also know that maintaining carbon requires continued inputs. This is a graphic by Peter Grace, where they've looked at modelling the amount of organic matter that can be retained based on your cation exchange capacity. Your cation exchange capacity is a good indicator of clay content.

If you'd like to look at the X-axis, or the bottom axis as clay content, it indicates that for a sandy soil, which has a cation exchange capacity of less than five, in fact it's about two, the model would predict we wouldn't retain any more than 25 to 30 per cent of the carbon that we put into those soils.

We know that there is a driver and if we looked at the long-term trials, which are actually from the United Kingdom, so it's from Rothamsted Research, but it provides a long-term outlook which we don't currently have within Australia. This shows on the left-hand side of that graphic a situation where manures were put on every year, I think at 30 tonnes per hectare, we get an accumulation of organic carbon in those systems. The control soil is the bottom, so that is a continuous wheat system, which is yielding about one tonne per hectare per year, has no fertilisers put in it. Put a little bit of NPK fertiliser on it, higher biomass, higher returns, you get slightly higher carbon.

But the important point for this graphic is where the manure amendments are stopped, so we're no longer putting in additional organic matter, that organic carbon starts to come back down to the equilibrium based on soil and climate. Where we are accumulating carbon and we want it to continue to remain there, it means putting in higher levels of carbon on a continuous basis. The interesting aspect of this other slide on the right-hand side is where the soil had less clay, so it was sandier. Regardless of the treatment imposed, all of those systems degraded soil organic carbon through time.

Back to Australian environments and this is a graphic of rainfall by soil organic carbon and you can see lots of variability in there; that's normal, that reflects the different management strategies and the different systems and climates we grow in. But you will notice that as you increase the amount of carbon, we're obviously in higher rainfall environment and where we're in the high rainfall environments, there is a much greater variability in the amount of soil organic carbon that's been able to be accumulated and that is largely a result of management. So, in those high rainfall environments which have the potential to grow large biomasses, those growers that are managing it well are managing to build high levels of soil organic carbon.

In the low rainfall environments, you'll notice that the variation is much smaller. The ability for a grower in a low rainfall environment, which is drying, is much more challenging in terms of building soil organic carbon and accumulating that.

Part of the difficulty in looking at climate and its influence on soil organic carbon is that it is interrelated with fit-for-purpose land use systems. In high rainfall systems, we are often looking at perennial pastures and pasture systems being dominant because they are less inclined to lodge and be affected by water logging as would occur in grain cropping systems. Part of it is a fit for purpose and part of it is related to what we can grow.

Looking forward, if we're looking towards drying climates, an example of a 30-year past rainfall system and the amount of carbon that's accumulated, so this happens to be for a high rainfall area in Western Australia, achieving about 60 tonnes of carbon per hectare. But if we look at the last five years of rainfall for that same data set, you would perhaps hypothesise that going forward and declining in rainfall, we might actually see a decline in soil organic carbon in those environments. So we need to consider what happens going forward.

I've mentioned temperature before. We know that temperature is highly influential on the rate of decomposition of soil organic matter. This again is a dataset from the same data as the rainfall, but this indicates that potentially there are environments where when the average daily annual temperature is greater than 17.2 degrees, in this particular instance, we are far more constrained in the amount of carbon that we can build. Again, it comes back to that climate driving carbon. Is that a critical limit for soil organic carbon potential? Does it differ from other regions? I think that we haven't answered all of those questions. But I've certainly heard some discussions that say, yeah, we're not so different.

If we took that information and we said, well where in Western Australia would we be challenged or more challenged in terms of accumulating carbon, you would look at the graphic on the right-hand side of the map of south-west WA and you'd say the areas in dark grey are those environments where the temperature and the rainfall are such that accumulating carbon in those soils is going to be challenging. It can be done, but it will be challenging.

If we looked at Australian influences and this is some work by Raphael Viscarra Rossel, they've been able to use the climate and soil type influences to map that out across Australia. It's a little bit different to see at this scale, but where you have the blues and the greens, you're essentially building or have accumulated more carbon stocks. The red map below is just our level of confidence or variation in those. We know climate influences decomposition; it influences how much vegetation we produce. Again, question mark around drying climates.

What I want to leave you with is the complexity of the issue that we're facing. We're talking about soil organic carbon here today, but soil organic carbon and accumulation of carbon is based on the premise of having a healthy plant with healthy root systems that is not impeded by such things as subsoil constraints, where you have subsoil acidity, where you have compaction, where you have high disease levels, they are all things that will slow root growth and therefore plant growth.

If you thought about carbon in the complexity of the soil, this is just a spaghetti map, it doesn't even show you all of the interrelationships, but we have carbon there in the green. But we change soil pH, we will change the amount of carbon we can accumulate. We change all of these interrelationships. Climate and temperate change will change them. The types of bacteria that are there will change it. So understanding the complexity of how those soil properties, environment and management interact is really critical in terms of knowing or being confident around what systems can accumulate carbon.

Leaving you with this example, it's a real situation. This is a soil profile from WA where we have not one, not two, but three significant soil constraints in place. We have a water repellent topsoil, it has lower infiltration, lots of the water running off, so it is impeding the amount of plant biomass we can grow. We have a soil pH at the surface, which is 6, that's reasonable, but when you go into the subsoils, it's below that critical point of 4.8. We've got subsoil acidity, we've got aluminium coming into solution, we've got roots that don't want to grow – that's if the water got in there to help them grow – and then we have an increase in soil strength. So, we have a compaction layer in the soil and roots have difficulty growing through anything that's above 2 Mpa. In this instance, where you're below 15 centimetres, your roots are using more energy to struggle through that really compacted, tight soil.

These are three constraints that, take the logical approach, what is your most limiting constraint in your paddock? If it's subsoil acidity, fix your pH and your roots will grow bigger, your plants will grow bigger, you'll have more inputs. If it's compaction, address that. There are a number of ways that growers, by making the right decisions and they are the right decisions for their economic business, for their yield productivity, are the right choices to build and accumulate carbon in those systems. It will be slow, but it is achievable.

I'd just like to leave you again with an advertorial, also the fact that GRDC actually did fund a physical book on Managing Soil Organic Matter for growers some number of years ago and that would be available, downloadable from their website as well as there is physical copies around. Thank you for your attention and I'll move on to the next speaker.

Summary: Parts 1B and 1C: The science behind SOC

What is SOC?

What is its function in the soil, linkages to soil health?

Impacts on SOC content

There are 3 main factors influencing the ability of a given soil type to retain SOC, these are:

Soil type - Naturally occurring clay in soil binds to organic matter, which helps to protect it from being broken down or limits access to it by microbes and other organisms. Increasing levels of soil acidity are linked to low carbon use efficiency in microorganisms, influencing the accumulation and decomposition of SOC.
Climate - In comparable farming systems with similar soil type and management, soil organic matter increases with rainfall. This is because increasing rainfall supports greater plant growth, which results in more organic matter accumulating in the soil. As the climate gets hotter and drier, organic matters build up can be limited due to productivity constraints and accelerated decomposition rates. Where soil moisture is available in warm to hot environments, decomposition occurs more rapidly.
Management practices – land and soil management practices can both positively and negatively impact of SOC levels. For example, maximising crop and pasture biomass via better water-use efficiency and agronomic management can increase organic matter inputs where sufficient inputs are retained. However, frequent large inputs of organic matter are required to increase SOC. It is possible in cropping systems that 'improved' management practices where measured through time, reflect a slower rate of loss rather than accumulation.

What is the probability of successfully increasing SOC?

Transcript

Mr Peter Wilson: All right, so we're continuing the Fran and Dan show. Perfect. I don't know if I'm allowed to say that. The Western Australian School of Agriculture and Environment, Professor Dan Murphy, not to downplay Dan's expertise at all. So, Professor Murphy has obtained his PhD in soil science and agricultural microbiology from the UWA whilst based at CSIRO. Very auspicious. Dan works closely with our last speaker and is currently the co-director of SoilsWest. He conducts research and student supervision that addresses issues relating to the development and sustainable management practices for agriculture and mine sites under rehabilitation. Biology and biochemistry of soil is a major focus of this research. Staff and students employ a range of tools to study microbial ecology and nutrient cycling. Dan will provide an overview on the biological processes and drivers for soil organic carbon, how it can be increased at farm scales and the probability of successfully doing it. Thank you, Dan.

Prof Daniel Murphy: Great, thanks very much and thank you for the organisers and the invitation to come and speak. I've just brought up my biscuits here from the table. Some of your might have eaten yours already. You have, haven't you, pointing down there. Some of you might have had breakfast this morning, some of you, like me, are on the wrong time zone and still waiting for breakfast. But my point is that we all have to take in food and one of the previous speakers made the point that we're reliant on farmers providing typically three meals a day.

So we're going to imaginary land in this speech, you're all now a microbe, okay? All of you are microbes and you're ingesting food. If we take something like a biscuit, we're going to eat it quite quickly, it's got a high sugar content and we're going to respire it off quite quickly. Would everyone agree with that? If we go and eat this lectern, it's nice and stable here this piece of wood because it's inside this room – we'll leave our biscuits down here – the lectern, if we took that outside and gave it water and we put it on the soil, so you as microbes could colonise it, fine, it's not going to disappear in the next day, it's not going to disappear in the next month, but eventually we will eat that and break it down and in doing so, we'll grow, we'll divide and we will respire.

One of the challenges we have is this reality that as we input organic matter, we're also microbes, we're respiring it and doing all those great things in soil that microbes do, recycle nutrients. We have to do that, plant-available nutrients come out of organic matter. Although we think a lot about carbon sequestration and there's obviously a very important political and economic reason for that, do bear in mind that the carbon, as Fran said, is only a component of soil organic matter. At the moment in the West, we've got Lego Masters on TV, so that's our Lego circle up there. Pick a colour, one of those colours is carbon, the other one's nitrogen, the other one's sulphur, the other one's phosphorus, the other one's potassium, the other one's magnesium and so forth.

Organic matter is a molecule based on carbon but contains nutrients. And as microbes as you break down that organic matter, we use the carbon as energy, we respire some of that out as carbon dioxide, which is what we're doing now, but we also take those nitrogen building blocks, those sulphur building blocks and make new cells. We have to remember that there's an economic value associated with organic matter for all of those other nutrients that are built into that building block that are tied up in that organic matter. We talk about organic matter, we talk about carbon, but remember it's a big molecule with lots and lots of things inside of it.

In those books that Fran mentioned, she put me in front of a bloody green screen, which I absolutely hate, because you feel really, really silly and she had me doing this. If you want three-minute version, look at the book, but you're going to get the 25-minute version now, because I have to simplify things and the way I simplify it is I don't think the different levels of organic matter are any more complex than a tipping scale.

One side of a tipping scale you've got inputs and that's clearly net primary productivity. How much organic matter, through photosynthesis, can we get back into the soil? That depends on what crops you're growing, it depends on the soil type, it depends on your fertiliser regime, it depends on temperature, as pointed out in the previous set of slides. The other side of the tipping scale is how fast are we working to eat that organic matter to break it down and to rerelease some of that as carbon dioxide, some of that clearly staying in the soil and helping to change that balance?

Look at your table, you've all got a glass of water in front of you, that's your soil, you're a microbe, that's your imaginary soil. The size of the glass is your physical storage capacity for organic matter in your soil. All soils here, on your table, are the same because everybody's got the same sized glass, so your storage capacity, your bucket, is the same. But look around, some of them are empty, some of them are quite full. Some of you have poured more water into your bucket, some of you have drunk out of it. Your organic matter balance is very dependent on not only the storage capacity but this point in time, how much have you put in and how much have you consumed. Of course, management and climate alter those aspects of the balance.

What I'm going to do now is go through some of those outputs and inputs and give you example. I've skipped water because I think we can all accept that without water there's no life, we don't live, microbes don't live. If the soil is moist, microbes are biologically active. One of the catches we have is you're all there breaking down organic matter every day, we need food sources every day. We can go for short periods of time without food, but not long periods of time. If the soil is moist, a microbe is doing its job, it is breaking down organic matter. But of course, in a farming system, we're not necessarily putting organic matter levels in at high levels every day. If you've got a pasture system growing every single day of the year, you have some organic matter going in with that live plant. If you're in a semi-arid environment, wheat for a winter crop, dry fallow over summer, you only have organic matter inputs for part of the year. But if there's a rainfall event, the microbes are breaking it down.

Now we're not that complex. Somebody mentioned about the complexity of a brain, you're not a human body anymore, you're a microbe, we're pretty blood simple biochemistry. We're a bit of cell wall holding a few chemical reactors together, not a lot to us, we're very, very susceptible to our environment, particularly temperature. With chemical reactions, as temperatures increase, chemistry tends to happen faster; molecules move faster. There are extremes. You'll get to a point where a microbe dies because it's beyond the physiological temperature that that microbe can exist. But here in this dataset, there's lots of soils through Australia that see surface temperatures of 40 degrees Celsius or above. Microbes tend to be faster, more active, as long as there's water present, at higher temperatures. As Fran pointed out in her slide, if you're in a higher temperature zone, your microbes are respiring faster, they're more biologically active because their biochemistry is just happening faster, that cell shunting, that cell biological processing occurs faster.

Here we have an example of stubble being retained or stubble being burnt. Different levels of respiration, that's just the carbon dioxide; I'm respiring now as I talk to you, you're respiring as you're sitting listening. Different rates of respiration, but you can see in this study very clearly going up as temperature increases. Not surprising, we can store a lot of carbon in the polar regions because they're frozen. Here, arid environments, high temperatures, it's harder to do that because it's being broken down as the microbial biochemistry kicks on at a very high, fast rate.

All living organisms have tolerances and one thing that affects biochemical processing, breakdown of organic matter, cell life, respiration, is pH. If we were dumped in hydrochloric acid or, as my kids tell me off when I pour the pool acid on my foot because I'm not wearing any shoes, it burns, okay? I have a physiological intolerance to acid or highly alkaline conditions. We live within biological environments and microbes are no different. Different types of microbes can tolerate different pH ranges, but as a general rule, microbes and biological cycling is quite dependant on pH. This is a little schematic, but behind that schematic drawing is 2000 data points in Australia looking at what's called microbial carbon use efficiency.

We've fed those biscuits to you as microbes and worked out how much you retain and how much you respire, a simple split. Are you keeping it as new cells and dividing and becoming a new me, or are you respiring it out? You can see that line changes and as we go from high pH to low pH, you can see that line, the area under the black, decreasing. At lower pHs microbes are less efficient at retaining carbon, so new cell growth, new organic matter and they respire out more CO2. So the way I convert that biscuit to growth or respiration changes depending on my pH. The reason for that is at low pH they're stressed and when you're stressed as a microbe, you don't grow, you respire more energy as you try to maintain your physiological state as you try to survive. Any stress environment means you will lose more carbon dioxide and you will convert less of that organic carbon to new soil organic matter. There's a change there on that figure of about 20 per cent, which if you think incrementally through years and decades, is a very large number.

Now let's think about the inputs for a minute. I think as scientists and as people that monitor things, sometimes we forget a little bit that we do trials and we look at the differences in our trials and we get very excited, but sometimes we have to think about timeframes and think about what the soil was like before we started farming, because we do get quite excited about treatment differences but let's put that into context. Here is a trial, this one's been going for about 30 years. There's some filled-in circles which is stubble retained. There's some open circles which is stubble burnt. Fran used this example, the little green part at the bottom of this slide I've taken from Fran's slides to remind you of what she said. No difference in soil organic carbon, 1.2, 1.3 per cent, not significantly different. Microbial biomass, yes there's a very large difference, so retaining the stubble has allowed us to grow, it's a more biologically active system.

But the take-home message that I want you to see from this slide is look at the decline through time. It didn't matter whether it was stubble retained in this case or stubble burnt, both of those farming systems are declining soil organic carbon through time. That site before it was farmed, 30-plus years ago, under a natural system, actually had a higher organic matter level. Both systems are running down; it's in a run-down phase. And the reason for that, again, the tipping scales: low rainfall, we grow very little plant biomass, low rainfall, less plant biomass, less photosynthesis, less net primary productivity; warm temperatures, rainfall, microbes are breaking it down. So in both of these cases, the carbon inputs are quite low every year and the microbial respiration rates are very high. That is a no-win system that is running down through time because we can't get enough organic matter into the system.

The only way of combatting that would be to import organic matter from somewhere else, like a compost, to increase your inputs. Then you have to think about all the budgeting about where you've grown that from and what that means for the other area of land. It's a bit of a warning that we have to think through time about how changes occur and organic matter is a decadal change in time, not an overnight change in time.

Another thing we have to do and this refers back to your glass and how full it is, is we have to think about the capacity of our system under the climate that we're in, or maybe thinking about future climate change if we're in an area where we expect climates to dry, for example, or rainfall patterns to change. But here is an example of a splattering of paddocks against rainfall on the X-axis and soil organic carbon stocks. Then there is a dashed line up the top. That dashed line is a modelled estimate of the storage capacity for those soils and later speakers will explain some of the carbon modelling, but scientists are pretty good at understanding how an organic molecule breaks down, how it respires, how it forms new organic matter. So, we're actually pretty good at modelling expectations of carbon storage in soils. It's not rocket science.

You have a line there suggesting as rainfall goes up, as you can grow more and more and more net primary productivity, you have a greater potential for increasing inputs of plant material to soil. On the right-hand side, not surprisingly, higher rainfall systems, a lot of them are pasture systems, perennials; lower rainfall systems, down in the 400s, you're talking about cropping. Each of those points is a real paddock. You can see some of the points in the top area are very high rainfall are above the predicted line. They're areas where we've got waterlogging. Waterlogged systems, if you think about through Europe and think about peatbogs, for example, waterlogged systems, lack of oxygen, your biological processing is slower as a microbe. In waterlogged systems, organic matter breaks down slower. In aerated systems, when you go and till up soil and make it nice and fluffy and lots of aeration, you break down organic matter really, really, really fast. That's the reason why some are above the line.

But the other thing to note is some of them are very close to that modelled line. That means that some of you have glasses that are nearly full to the top, so you've actually almost sequestered your bucket's capacity for that soil type under that climate. Some of the other points have only a little bit of water in your glass, your bucket still has a lot of capacity. As part of the challenge and part of what I think will become a challenge in terms of making generalisations, is how big is your bucket, what soil type and rainfall are you under, what is your current level of that bucket being filled, past management practices, what is the difference is the capacity we're playing with. So there will be some farms out there that might be very, very good farmers, but will have little capacity to sequester more carbon because their bucket is almost full. There'll be other sites where there's a larger capacity to sequester it. The challenge is finding where those areas are to really get the biggest bang for our dollar.

Now I've said you're all microbes, you've eaten those biscuits and you've already started breaking that down by now and respiring out CO2 and the reality is, whether we like it or not, microbes actually remove a lot of the organic matter from the soil back as CO2 and actually evolutionarily we needed that. Photosynthesis, plants have evolved to capture carbon dioxide and put it into the soil as organic matter. Microbes do the other half of the circle; they break that organic matter down and rerelease CO2. So a natural cycle is inputs of carbon through photosynthesis, outputs of carbon dioxide through microbial respiration. That works perfectly well until we came along as a species and started changing that balance with the Industrial Revolution. But it works in principle; you have to have microbes breaking down organic matter, otherwise it all goes in and it never comes out.

The catch and the constraint we have is a lot of what we put in comes out as carbon dioxide. This is an example here. Every one of the blue arrows shows 20 tonnes of extra plant residue. I've put the extra in capitals because this isn't your one or two or three tonnes of crop residues from growing the crop, this is us actually getting extra lucerne hay, buying extra hay and bringing it in and importing in about 20 times the average. This isn't a management practice that a farmer, a grower would ever use, this a research example. We've supercharged the inputs of net primary productivity, we've made that tipping scale of inputs as high as I can reach, 20 times the normal and you can see those blue additions. The grey line is the normal state, just status quo in that paddock and organic matter levels are floating around about 0.8 per cent, this is a very sandy soil. You can see where the inputs have been in, there's ups and downs. Those ups and downs are a challenge for monitoring because there are ups and downs depending on annual inputs and annual respiration rates and annual temperatures and annual rainfalls, but we can see a difference at the end over that period of about a decade or 13 years.

So organic matter has changed where we've supercharged the inputs. It's gone from 0.8 somewhere around to about 1.2, so we have changed organic matter per cent carbon, we have increased it. But the reality is that if you look on the bullet points on the side, what we've ended up with is for that 20 per cent, we've added in an extra 48 tonnes of carbon, 100 tonnes of lucerne hay, about half of it being carbon, 48 tonnes of carbon have got in extra to the system normally receiving it, about 20 times. That's increased the carbon stock by about 7.4 tonnes of carbon per hectare over 13 years, so it's a decadal increase. Do the maths, that's a 15 per cent conversion rate. So as we ate those biscuits, we have kept 15 per cent of that biscuit for new growth and we have respired out 85 per cent of that biscuit into this auditorium. The challenge is a lot of what we put in comes back out of the system as microbes break it down.

I've made this mention to your glass and the size of the bucket, again another modelled line using carbon modelling, so that line at the top, that solid line, is attainable carbon storage, what the modelling suggests is attainable for that soil type under that climate. It's modelling inputs, it's modelling respiration, it's modelling that budget of the tipping scale just doing it a lot faster than I can. What you can see here is growth of perennial pastures, so this has gone from a cropping system before day zero and up to about 35 years they have been putting in perennial pastures, trying to get more carbon into the system. The first thing you note is each of those paddocks, which are individual paddocks, different farming systems, different farmers, are all over the place, some are high and some are low. There's a lot of variation in soil organic matter data, even within one land use, being perennial pasture here.

I've highlighted some of the values. They're out at 30-plus years, but they still have very, very low soil organic carbon levels, so you have to start asking why. We've been putting perennials in for 30 years, why are our soil organic carbon levels still quite low? Well in those particular cases, they have other constraints to production. The perennial plants aren't in an optimal soil, they're not happy, they're not growing to their maximal biomass because in these cases they've got other problems. There's a boron toxicity problem in some of this area, which is quite atypical to a lot of Australia, but roots don't like the boron. There's some acidity problems down there. Plant roots don't like high levels of aluminium. So, there are reasons why plants don't grow to 100 per cent of their water use efficiency. If we could take all of that water and convert it into plant growth, we're maximising our ability of that photosynthetic cell to make organic matter.

Wheat production in WA, I don't know values for the East Coast, but we sit at about 50 per cent water use efficiency. In other words, the plant receives two times the amount of rainfall than it actually converts into plant biomass. So, we're not maximising our capacity of growing a plant, we're not maximising the inputs because we have soil constraints. So, one of the things that we need to overcome is what are the limitations to growing a plant, because that is constraining the limitations of growing organic matter. Some of these sites you can see along that solid curve are very, very close, their bucket of water is completely full, because clearly in those cases they are maximising plant growth for their location, they clearly don't have major soil constraints, they are converting as much photosynthetic material as they can into new organic matter. So, our challenge is, where do you target carbon sequestration? You don't target it at the ones that are already full, because they're already full. You don't target it at the ones that have lots of other constraints until you remove those constraints. So there's a sweet spot through the landscape of trying to really identify the optimal areas.

This is my last slide. I just want to reemphasise this point, that even when total carbon levels don't change and I clearly understand that from a carbon accounting point of view that's what we're after, we're looking for areas where we can do that, but do remember that organic matter is not only carbon. Where carbon levels don't change, that doesn't mean the two soils or the two management systems have the same level of soil health, have the same level of biological functioning. Here is an example where there are three treatments, conventional farming practices where they were doing some soil disturbance; no tillage or minimum tillage, whatever you want to call it, where you've got rid of that physical disturbance of the soil that helps to aerate the soil, helps to break up aggregates, helps to break down organic matter; and then from a research purpose, a rotary hoe, so a rotary hoe out of horticulture, you've mixed that soil up completely, given it 100 per cent mixing, you would never do that broadacre, but it's just there to try and really maximise aeration and maximise organic matter breakdown.

This is only after 10 years, it's not long term for organic matter change. I've already said organic matter often doesn't change within a decadal timeframe. It's a long game. But here we can see total organic matter, two soil layers, basically the same, no significant difference. Those systems are not behaving the same though, even though they've got the same organic matter level. If we look below where it says microbial biomass in the yellow and the red, split into two layers, five centimetres and five to 10, you can see that as we've increased disturbance, as we've increased tillage, we've gone from a higher value under conventional to a lower value under rotary hoe. Those As and Bs are indicating significant differences. So the rotary hoe effect has decreased our biological capacity in the soil; it's decreased the number of microbes, although the total carbon value is still the same.

Fran mentioned what she called particulate organic matter or that more labile fraction, I've used the term labile organic matter. Particulate and labile get reversed and used both in the literature, so be aware of that. But again, you can see here there is some evidence that under the no-till system, there's a more labile fraction of organic matter building up, so the new input into that system is more biologically available, more labile, it's newer plant residue coming in versus the old stuff that's been there for the last 100 to 10,000 years. A challenge we have with carbon sequestration is a lot of the new organic matter we're building starts off in those labile fractions, so it's more volatile to breakdown by microbes before its processed and processed and processed over decades and centuries into that really, really stabilised organic matter that's going to hang around for a millennia.

So, there is a challenge in understanding the fact that microbes are on the counter side to what we want to do. We don't want to get rid of them, they're breaking down organic matter, they're releasing nutrients, they're allowing your soil to function, we want the microbes to be there, but in doing their job, they're respiring out carbon dioxide and that carbon dioxide is what we're trying to sequester by putting in more plant inputs. Those tipping scales have to be balanced in favour of inputs of plant material not outputs through respiration or of course through erosion. That's our challenge, is to increase inputs while managing that biological functioning which, by definition, is using organic matter as its food source. Thank you very much.

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Dr Susan Orgill, Soil and Water R&D Unit, NSW Department of Primary Industries.

Permanence in soil

SOC comprises humus, microbes and decomposed resides, and charcoal. Humus is largely composed of microbial detritus. It is more resistant to degradation than particulate (partially decomposed carbon) and it is nutrient rich. To increase humus, soil microbes use nitrogen (N), phosphorus (P) and sulphur (S). SOC can be built by maintaining higher levels of organic matter inputs and using appropriate management practices to protect it. Replenishing SOC in the soil may be slow and unspectacular, however it IS achievable and management practices need to ensure this potentially more vulnerable SOC is not rapidly lost.

Vulnerability to Loss

The focus on SOC tend to be on how to accumulate it rather than preventing loss of SOC stocks. However, the same factors that influence accumulation also influence loss. The level of soil carbon in soil is determined by the balance between inputs of organic matter, and its subsequent rate of decomposition and loss. Organic matter cycling underpins production, so not all loss is bad! What is important is that the balance favours more organic matter entering the soil, than leaving it, and that the loss via erosion is minimal (zero!).

Rates of decomposition are affected by:

Temperature
Rainfall (frequency, intensity and amount)
Water and atmospheric balances—aerobic or anaerobic systems
Soil biology
Management practices
Types of organic matter

Impact of climate change on soil carbon stocks and flows

Variability in temperature, rainfall, water and atmospheric balances can have a major impact on stocks of SOC. Therefore climate change will be an important limiting factor for the ability of farmers to build and maintain SOC stocks across the agricultural landscape. However, it is still critically important to focus on increasing more stable forms of SOC, maintaining higher levels of organic matter input and enhancing the protection of SOC through good soil management.

Transcript

Mr Peter Wilson: Our next speaker, Dr Susan Orgill, NSW Department of Primary Industries. Susan's been there since 2005 and is currently a Research Officer in Soil Carbon. Field of research relates to improved organic carbon accumulation and storage, nutrient cycling in agricultural soil and management practices that contribute to the increased economic and environmental outcomes for New South Wales. She completed her PhD through Charles Sturt University in which she investigated the effect of perennial pasture management on carbon accumulation. Susan will talk about how we can keep carbon in the soils, the vulnerability of those carbon stocks and the impacts of climate change. Thank you, Susan.

Dr Sue Orgill: Good morning everyone. I was a little bit nervous to be up here speaking. And then I saw Gus and Kelly's property up there and that's a property that I work on with NSW DPI and they're doing amazing things and it definitely made me feel more comfortable. That, and that when I told my six-year-old son this morning I was a little bit nervous speaking in front of a whole lot of really important people, he's just like, "Hello, I'm singing in junior choir this morning in front of some year six students." And I'm like, okay (Zavier 01:27), yep, right, perspective, it's all about perspective. I'd rather be speaking with you guys than singing in junior choir, I can tell you that for sure.

The question that my presentation will be addressing is, if soil organic carbon increases, will it stay in the soil? And there's three key components that I want to talk about following on from Fran and Dan and Liz's presentations this morning. And that's around permanence and permanent forms of carbon in the soil, the vulnerability to loss, so what makes soil organic carbon vulnerable to loss from the soil, and also the impact of climate change on those soil organic carbon stocks and flows.

To begin with, I'd like to recap on what we've heard about this morning. And this sets the scene for when we're talking about permanence with regards to soil organic carbon. And that's around the flows of soil organic carbon around the landscape. It's not just about stocks, but it's also about flows and that's what we've heard. We know that carbon enters the soil though this process of photosynthesis, this billions of years old technology that we're still using, it's pretty tried and tested, and it works. And we have this accumulation of organic matter from above ground sources and below ground sources. When that's in the soil, we refer to it as soil organic matter.

Once it's in the soil, there's various pathways that that organic matter can take. It can be protected within aggregates, so soil crumbs, so that's protected from decomposition. That aggregate might be located deep in the soil profile, so it could stay there for even longer, even though we might take that soil sample out of the field, back to a lab, crush it up, sieve it, analyse it, and say it was labile, if it's protected within the soil structure and in the soil profile under a perennial pasture, we know that it's residence time can increase. We've also got chemically protected organic matter, either through its nature itself, so in char or humus that we've heard about, or through its association with clay particles. And then we've got the really important driving force of microbes in our soil as well, so the microscopic livestock which play an essential role in agricultural production and environmental health. But this is a flow of carbon around the landscape, so we've also got carbon dioxide leaving the soil, so it can leave through soil and plant respiration and it can be removed from the soil in terms of soil erosion, so the carbon that's associated with soil particles can leave that site as well.

If I was me, and I frequently am, there's three key things that we could focus on here. We've got permanence in the soil. Can we influence the fraction of carbon that's accumulating in the soil? Can we maintain a higher level of organic matter supply to the soil, so we have a permanent shift or increase to the carbon flow into the soil, so we're influencing the top arrow there? And can we actually protect the carbon from some of this loss, so reduce soil erosion and protection carbon in the soil, and alter that decomposition process?

Let's start on this journey together. The first thing I want to talk about is increasing the different fractions of soil organic carbon. What we've heard about this morning is that the most sensitive fraction of carbon to land management is that labile or particulate fraction, so it's most sensitive to management change, and we've also heard that it's the tastiest part to the microbes as well. It's the fraction that builds most rapidly, but it can also decline very rapidly as well. If we use this example here from Jeff Baldock's team at CSIRO, it's looking at a simulated example of a wheat-fallow rotation and it gets changed at about 33 years, you can see, to a permanent pasture.

If we first of all focus on the top black line, we can see under the wheat-fallow rotation, we have this steady decline, and that's consistent to what we've heard from Fran and Dan this morning. That decline happens in the total organic carbon and it can also happen in the fractions as well. If we look at the green line, we can see that's the particulate, the tasty organic matter, it declined most rapidly and within about five years. Once we return to permanent perennial pasture, we can see that it's the fraction that responds most rapidly and you get this quick exponential increase for about five to ten years in that particular organic matter fraction. Humus, which is the more stable fraction of carbon, however, you can see increases at a slower rate. We know that the fractions of carbon are important. But what I take away from this is we also know that management's important. Management is that lever that we can actually pull in this example.

If we think about pulling one of those levers, to use that term, something we can focus on is humus. We've learnt this morning that humus, the more stable form of organic matter in the soil, is made up of microbial detritus and it's nutrient rich. And that's why it's so important for agricultural production and environmental health. We also heard that microbes, they use carbon as energy, but they also need nutrients as well. Instead of referring to carbon here, in this sense it's really important that we talk about soil organic matter and the humic fraction of soil organic matter because it requires nutrients as well. With our residues that go into the soil with our management, be it a crop or a pasture, generally they're quite carbon rich, so the microbes need to use nutrients. And sometimes this is where we'll hit a nutrient wall, so the accumulation of humus might be limited by the amount of nutrients that are in the soil. But the amount of nutrients that are in the soil is something that we can manage, right.

If we want to increase humus, that stable fraction of organic carbon, we can think about how we can influence the nutrition of soil and build on that carbon use efficiency that we've heard about this morning. Another way that we could look at influencing the stable fraction of soil organic carbon is by bringing stable products to the soil. And an example of that is biochar, but it could also be stable compost or other products like that. Biochar is fine-grained charcoal products and it's produced under a low or a no oxygen environment. The beauty of it is you get energy, and you get a soil amendment. And that soil amendment is carbon rich.

In this graphical abstract here – it's like graphic, you expect it to be a little bit scary, but it's exciting – so what we can see is if we have residues being returned to the soil, while it's very beneficial for soil microbes, we might have no net change in soil organic carbon. And that's consistent with some of the data that has been provided this morning. However, if we add the same weight of carbon to the soil in terms of biochar, which is very stable and its degree of stability depends on the intensity of pyrolysis that it's been through, makes it more resilient to decomposition or degradation, we can not only influence the priming that happens in the soil, influence those biological cycles, and have a beneficial impact on soil condition and health, but we can have a long-term soil carbon story. That's one example of where we can actually bring a product to the soil which creates stable soil carbon.

What I think really gets me out of bed in the morning is maintaining high levels of organic matter input. How can we increase organic matter input and protect it, so it stays there for longer? And farmers are really clever at doing this. The example that I'd like to use here, and there's lots of examples about land management benefits for increasing soil organic carbon, but the one I've selected is a long-term trial that DPI ran just south of Wagga Wagga. On the X-axis we've got the years and in the Y-axis we've got the tonnes of soil organic carbon to 30 centimetres. Now, what I'm going to show you, the As here refer to annual pastures, and the Ps refer to perennial pastures with and without lime. The minus just means it didn't have lime applied. The plus means it did have lime applied.

Now, a bit of a background on this site, it was a low carbon site to begin with, so the lower the carbon starting level, generally the more sensitive to the management change and the greater the increase you can get in soil organic carbon, right. Your bucket's already empty, easy to fill it up. The next thing to remember is this was a reasonably degraded paddock of an annual based pasture. It was acidic and it was (indistinct 10:24). It's what we refer to in soil land as a (crapper soil 10:28).

Let's have a look at what happened. After these trials, replicated trials, it's published, it's all legit, right, what we can see is, with including a perennial or an annual pasture that's well-managed into the system, we had an increase in soil organic carbon. Now, two things I want you to take away from this. First thing is, there's a fluctuation, right. Can you see, it's not a nice straight line for Susan, it bounces around, and that's just what happens. These are complex systems, as Liz said.

The next thing that I think is really important to note – I keep going to point at that one, but you guys are looking up here, so if I point up there, that's not going to make a difference – is, if we kind of say the millennium drought is from around 2000 onwards, what happened to soil organic carbon levels? Have a look. Have a think. A lot to take in because it's a steep curve. They still kept increasing, right, because we had maybe the organic matter supply was limited because it's a rain limited environment, but we had protection mechanisms there to maintain that enhanced carbon sequestration, which was really important. When we average out the sequestration rates over the life of the trial, it was about half a tonne per hectare per year, significant.

Now, let's think about vulnerability to loss, so we go, right, we can increase permanent carbon, we have land management strategies in our toolbox to have that – maintain those high levels of organic matter input. Now let's think about what makes that carbon vulnerable to loss? What can we do, what are the levers we can pull to influence that? We've heard this morning that decomposition is a factor of management. Microbes and the type of microbes. The type of organic matter, how tasty it is. We all eat the biscuits first, not the lectern, right, agreed on that. Although I did see a bite mark, I thought. Anyway, the soil's capacity to accumulate and protect carbon and the environment in which we live.

Everyone who knows me knows what I'm about to do. Very quietly, I'd like everyone to stand up because we're going to do something, because we're sitting down for a whole day, so everyone stand up. And I would like to welcome you to our soil environment, okay. This is our soil. We've even got fungal hyphae hanging off the roof here, right. Those of you who know what it looks like, it looks very much like that. Within our soil environment, we have a range of particles, and we have been talking a lot about soil texture and clay, but basically within our soil environment we have particles of different sizes and the soil scientists, we refer to that as soil texture. And it's the proportion of silt, sand and clay, so look around the room and we've got people of all different shapes and sizes. We're not judging, just looking around. All different shapes and sizes. This is our soil texture. This is the proportion that we're dealing with. This is really hard to influence. In South Australia they add clay and do stuff like that, but up here we don't. This is what we've got to work with, and this is our soil texture. Now, if you can't influence that, what we can influence is our soil structure. With the same amount of people in the room, I want you to, in a very COVID-safe way get a little bit closer to your neighbour, okay, a little bit closer. We have the same amount-----

[Crowd noise]

No talking though. Soil particles don't talk, I forgot to mention that part. What we can see is the same amount of particles. What we've changed is the structure of the soil. This is what land management can change. If I'm a plant root now or if I'm a microbe hanging out with Dan, now we've got microbes and plant roots which can move through the soil and they can access water and nutrients, and that's good for – and air, and that's really good for production. It's good also for accumulating that root biomass, which is important for building humus, and particularly organic carbon. The next thing I want you to do, we've got our good soil structure, this is our soil environment, if you have a C for carbon in your name, if it's your first name, your middle name or your last name, I want you to put your hand up. Alright. These are now our carbon-based molecules in the soil.

Now, if we want to protect these people with their hands up, they can either be hanging out in the soil not protected, which means that they're going to be vulnerable to predation by those microbes, or you could have them associated with clays in the soil, so we have these organomineral associations which protect organic matter. We can't really influence that, I said. What we could do is we could occlude them, but we're not going to – no hugging, right, no hugging – we could occlude them within our soil structure to protect them. Land management – keep your hands up – land management – this is good for your circulation as well – and we're breathing out carbon dioxide so the plants are thanking us, atmosphere less so – land management can influence protection. This is important for permanence. Now, I want you to put both hands up if you eat food, wear clothes and breathe air. You're all part of the solution and I wonder if I'm the first person in a national press club to make everyone put their hands up.

The factors that we've just spoken about are also the factors that influence productivity, right. It's a win-win. Why we've got these challenges and complexities, I want you to be thinking about what we can actually influence and what those levers are. We know that soil loss via erosion is a major issue, so if we look at this global representation here. Here, the colour and the intensity of that colour represent the magnitude of loss. Within Australia, because this is a global representation, within Australia, we can see that annually in our kind of lower rainfall areas, we've got a loss of carbon from about one to ten kilos per hectare per year of carbon, based on these estimates here. That's determined by things like groundcover, soil moisture, the amount of carbon in the soil, so the enrichment ratio, so how much carbon is there to be lost. This could be quite alarming. But then, it can also be a role that we can play, right, through land management, and these are some examples taken from Western New South Wales where land management can promote that cover. If we've got carbon being lost, so therefore it is less permanent, it's being removed from the system, we can have an avoided loss of soil organic carbon through promotion of practices which keep a cap on the soil. Now that cap on the soil is also the same thing, the plants which put carbon into the soil.

Not all soil organic carbon loss is bad though. We heard this morning that our agricultural production systems actually rely on organic matter cycling because with that cycling comes the provision of nutrients which plants rely on. In this example here, if we think about a crop pasture rotation, so where you have a few years of pasture, then you go into a few years of crop, what you have is you have the build up of soil organic matter, we know that's carbon, nitrogen and other stuff, and then when we go into the crop, we have the agronomic use of that soil organic matter using the nitrogen and we get that rundown phase. What we can manage here is we can make sure that we avoid that net loss of organic matter, but also really importantly, we can make sure that we're providing organic matter through our pasture phases so that we have less requirement for nitrogen during our cropping phase. This is a really important role of using soil organic matter and making sure that our pasture and crop rotations are such that we're actually building on the stocks and making sure that we're not going below that lower limit.

An example of that – this is pretty much what I just showed you in my very simple diagram, so this is a trial again from Wagga. The W means that it's wheat, that's the open columns that you can see there. The pastures are the solid columns. You can see, when it's under wheat, the open columns, the nitrogen stock, so this is nitrogen, goes down. When we go into the pasture phase, the nitrogen builds up. Then when we go back into the cropping phase, it goes down. This is the agronomically desirable use of soil organic matter, so not all loss is bad. What is important, like Dan said, is it's about the balance, right, making sure that we're not losing more than we're putting in.

We know that soil type and climate influence carbon sequestration. This image is from one of DPI's productions which is looking at sequestration and emissions reduction. What I want you to take away from this is, if we start at the top, we've got different environments. We've got dry environments in Australia, moist environments, and wet environments, and we know that rainfall drives production, and it also drives decomposition. We know for the next layer down, that cover, groundcover, the type of cover and the amount of cover influences how much organic matter goes into the soil. Now, the length of the bars with the soil type, which you can see for more sandier soils or more clay rich soils, indicates the sequestration potential. But it can also influence or indicate the decomposition rate that you could have if you actually shift those climates. When we're thinking about a shift in climate change, we're thinking about moving maybe from the wet to the moist or the moist to the dry. We might actually be putting less carbon in the soil and we might actually be influencing the rate of decomposition. We know that it's driven by rainfall and we know that for the example of New South Wales, it's becoming hotter and dryer and we've got these changing patterns.

Now, the two images that I've got – the four images, sorry, that I've got here from a very clever climate scientist at DPI, Dr Bin Wang, and what he's (running 20:45) in the top two maps is looking at a middle of the road emissions scenario. The next one down is the fossil fuel emissions scenario, so a higher emissions rate. And we're looking at the change in soil organic carbon stocks, so tonnes of carbon per hectare to 30 centimetres under these different scenarios at 2050 and 2090. The more intense the colour, the more yellow or the red, the greater the loss. We could use these maps, and we can see from these maps that really, in those hot, wet environments of the north coast or in those cool alpine environments, that's where we might be seeing the greatest change. We can use these maps strategically to target where resources and decisions and practice change can happen.

To sum up, for my last couple of slides, I have got some quotes. I went to some producers that I work with who I greatly admire, and they're innovative and they're the boots on the ground, and I said, "How do we keep carbon in the soil? Why would you actually do it?" While you guys read those quotes, and I've got one more slide after that of quotes, I'd like to recap. We know that we can sequester carbon in the soil, and we know that permanence can be an issue. There's these challenges. But we also know that climate change is a critical issue, and we have to act now. Part of solving that critical issue is taking the complexities and the challenges that we know about this system, but also working with producers to come up with some of those solutions. When we look at what some of those solutions might be, we've got some really big levers to pull to make carbon stay in soil, to make those increases more permanent. And you've read some of the quotes, but I'd like to end my presentation by inviting David Marsh up, who is a producer from Boorowa, to say in his words why we should keep carbon in the soil.

Mr David Marsh: Thanks, Sue. I'm just going to tell you a one-minute summary of what I've been up to for the last 22 years. Twenty-two years ago, we had a philosophical change of heart. We moved away from the economic relationship we were having with the landscape, did some training and started managing – making holistic decisions. And in the last 22 years, 12 of those years have been below average rainfall years. During those dry years, we have never lost groundcover because of our management. We've been matching our livestock to the grass. We haven't suffered any erosion either from wind or water. We haven't spent any money feeding livestock and we haven't sought any assistance from the government. And yet, the government's not knocking on our door to ask us how they could invest in this sort of agriculture. Our management always allows the inherent capacity of ecosystems to be more diverse over time and it allows that to happen because of the recovery we allow for our pastures. Diversity is absolutely key for us, and it's increasing on our farm with management. This is what we're trying to create, is a true profit, that is, increasing natural capital over time, including organic carbon, an economic profit, which we need, and people with improving health and wellbeing.

I'd like to dispel the myth that a barrier to adoption of this type of agriculture away from conventional agriculture – it's been put out there that the barrier to this is the high cost of transition, and that is absolutely the opposite to what it is. I see myself now as an observer of the landscape healing itself. It's becoming more diverse because that's been the trend of evolution since life began. The trend of evolution has been to elaborate and diversify the biota. And seeing that happen on a farm is incredibly calming to the human psyche and our agriculture needs to shift from something that's a mining operation to – the outcome of our management as farmers has to be a landscape improving in health and diversity, not the opposite. It's very calming on the human psyche and I think every day should be Earth Day. Thank you.

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Professor Peter Grace, Centre for Agriculture and the Bioeconomy, Queensland University of Technology. Note the presentation was delivered by Dr David Rowlings.

Considerations of GHG emissions when increasing soil organic carbon (SOC)

Agricultural practices which promote soil carbon sequestration may also produce greenhouse gases (GHGs) such as methane (from animals) and nitrous oxide (from nitrogen fertilisers) both having much greater impacts on global warming (per molecule) compared to CO2. For example, restoring degraded pastures will increase both plant production and soil carbon sequestration. However, the increased pasture growth will potentially support more livestock per hectare, producing more methane per hectare.

Previous Government research on agricultural GHG emissions and SOC

Australia has a large store of soil carbon and greenhouse gas emissions data from the Carbon Farming Futures (CFF) program. However, most of it is based on point source information, not spatially integrated, the latter being a major constraint with respect to accurately determining net carbon credits in agricultural systems.

Effects of increasing SOC on nitrous oxide (N2O) and methane (CH4) emissions

These non-CO2 emissions must be accommodated in any final calculation of soil carbon credits and whilst inventory-based data exists, they are highly generalised and based on industry wide emissions estimates. For example, nitrous oxide (N2O) emissions are heavily dependent on regional/carbon estimation area (CEA) specific soil type, climate and management interactions, as is soil carbon sequestration. Methane (CH4) emissions from animals are also dependent on the quality and quantity of feed on offer which likewise is soil, climate and management dependent. Spatially integrated emissions data at the CEA scale will reduce the cost of participation for farmers and provide global credibility with respect to measurement, modelling and verification.

Transcript

Peter Wilson: The next speaker, who is now Associate Professor David Rowlings from the School of Biology and Environmental Science at the Queensland University. David is a soil scientist in the Sustainable Ag program. His research is at the nexus of environmental and agricultural science enabling high-impact research outcomes for the benefit of both fields and positive change and food security. This talk is prepared in conjunction with Professor Peter Grace, who unfortunately could not join us today. And David will discuss how to account for non-CO2 emissions, the consideration of other greenhouse gas emissions when increasing soil carbon. Thank you.

A/Prof David Rowlings: Unfortunately, Peter couldn't be here today, so I'm stepping in in his stead. That was a pretty hard act to follow from Sue, so I don't think I'll talk about carbon anymore, I'll talk about other gases. And just to complicate things a little bit more, some more additional considerations we need to take into account when we're looking at, you know are we actually sequestering carbon in our ultimate goal of basically offsetting climate change. There's been a lot of talk about carbon so far, it's all about carbon, carbon, carbon. Carbon's great. But it is a little bit more complicated than that because there are some other non-carbon related gases out there called other greenhouse gases, which we need to take into account when we're having a management change. Carbon soil sequestration is basically about getting the carbon into the soil, but to actually get a carbon credit, we also need to take into account these non-CO2 emissions, so we basically need to account for them and minus them from the sequestration that we get from the carbon. Obviously, if we have a lot of these non-CO2 emissions, we get a pretty big discount.

However, there's two aspects to this. One of them actually is we need to take that into account, so if we are moving to a new system which is potentially, say increasing more nitrous oxide, we need to basically account for that and minus that from our carbon sequestration. But it also gives us an opportunity to refine our practices so we're emitting less of these other gases as well, so by reducing our methane emissions and reducing our nitrous oxide emissions.

Very basic carbon cycle. We talked a lot about how carbon is sequestered. Dan's got his balance. Nitrogen's been mentioned a few times now. Nitrogen is very important, they're very linked to carbon, as the slides before show that for every 100 kilograms of carbon sequestered, we need nine kilograms of nitrogen. Unfortunately, what happens is that in the soil, these greedy little microbes that are floating around there, they're very efficient at basically grabbing that nitrogen and securing that nitrogen for their own purposes. And what happens is that under certain conditions we can basically, instead of being able to grab oxygen from the air, they'll grab the oxygen from the nitrogen, and they'll produce nitrous oxide. Nitrous oxide is a pretty potent greenhouse gas. We get it when we have fertilisers, in fertilised systems it's a major source of the greenhouse gases. We get it when we have pasture renovation because that release of nutrients from the organic matter also releases nitrogen. That nitrogen then becomes available to the microbes for (indistinct 03:50) losses. And we also get it from other organic sources of nitrogen, so that's manures and whatnot as well.

Another one is methane. Methane is obviously well-known for its role in enteric fermentation in cattle. It's a big issue. But it's also produced in rice under anaerobic conditions, when the soil is waterlogged, but also under poorly structured soils where those soils become waterlogged and we're basically getting our carbon loss of methane as well.

There's a few win-wins we can actually achieve with this. We can reduce some of these emissions by improving our soil structure, as Sue basically said, the more you guys hang together, the better the water can go into the soil, the less waterlogging we have, so potentially the less methane we can produce. And also, with the nitrogen fertiliser, if we can replace those sources of really available, rapidly available high-turnover nitrogen with slower sources such as manures, we can also reduce our nitrous oxide.

When we do this, and particularly when we're looking at a change in management type, we sort of talk about these concepts like pollution swapping. We need to take into account the life cycle assessment. But another way of quantifying the complete impact that these managements has is called global warming potential. It's basically a measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It's a relative scale. It allows us to basically compare everything back to CO2, so if we're sequestering one tonne of carbon, compare that to CO2 in our soil, we know actually when we have the same units, when we start to compare in this other greenhouse gases. And as you can see, methane, 28 more times potent as a greenhouse gas than CO2, so that's important for the livestock industries. And nitrous oxide, 265 times more potent as a greenhouse gas.

Some of the management systems that they're looking at trying to improve soil carbon sequestration, particularly in the northern Australia where we do a lot of our work, are around let's look at pasture renovation, let's see if we can get better pastures, get that biomass increased so we can get our carbon back in the soil. Unfortunately, by doing that, we often (mineralise 06:11) that nitrogen or release it from the organic matter and in that conversion process itself, we can actually lose a lot of nitrous oxide. Some of the studies have actually shown we can lose 30 kilograms of nitrous oxide during this process. It doesn't sound like much, 30 kilograms. But when you times it by 265, you're basically looking at you might have to wait two or three years just to offset those changes during the conversion process in soil carbon sequestration rates. At the same time, if you're developing a land use change which increases nitrogen fertilisation through maybe putting on more nitrogen fertiliser, this is an ongoing discount you need to take each time because you're basically going to be getting losses through that nitrogen fertilisation process.

To put this in perspective, we emit in Australian agriculture 75 megatonnes of CO2 equivalence. Agriculture represents about 14 percent of all Australia's greenhouse gases. At the moment – and I say at the moment, 59 percent of that is methane, so that's the big one. And if you're the beef industry or the dairy industry, that's the big one. Those guys have been pretty proactive and there's been some really good home-built Australian ingenuity around (indistinct 07:28) and feed supplements that can reduce that methane. And some of the trials are showing that we can reduce that methane by 90 percent. As we reduce that methane by 90 precent, these other ones start to play into it, become more and more important into the Australian greenhouse gas budget. And particularly all nitrous oxide. Australian soils emit about 86 percent of all nitrous oxide emitted in the Australian greenhouse gas budget.

Once again, a bit of perspective around methane, and this is important because if we're looking at increasing productivity, which everyone wants to increase productivity, we want to do things that are hopefully not only sequestering carbon, but we can also increase the productivity, we also need to account for the emissions associated with that increase in productivity. Just a rough rule of thumb, for every additional animal we put on there, one dairy cow equals three tonnes of CO2 equivalence. If we're increasing our stocking rates or our intensity by one – we can carry one more animal per hectare, we need to offset an additional three tonnes of CO2 equivalence. This is a bit of a loophole in the system unfortunately at the moment because these, across the whole industry there's sort of a set bar based on markets and we can't keep increasing animal numbers indefinitely. There has to be the people to feed them. But at the moment, the way that the system works as far as the carbon credit market goes, we basically need to account for this increase in productivity. And obviously, the equivalent to that in goats and pigs is much, much less, but the enteric methane in cows basically accounts for a lot of methane being produced.

Once again, a bit of a summary of how these processes are formed. We have our CO2 budget in and out. Most of the time, as we've seen, it's actually pretty neutral. However, these and the soil carbon that is accumulating in the soil, if we can manage to get it – and what we're talking about here is not so much an emission, it's basically this is a one-way path. We're actually losing these from the soil. It's not like soil carbon, where it has to stay there, if we get it in the soil, we have to keep it there. If we can stop these from being produced at all, it's basically a one-way street. They never were produced in the first place, they would never have become an issue for the global warming potential. They're mainly derived around that nitrogen that goes in the inputs and then cycles through the organic matter in residues, soil organic matter, manure, urine and various loss pathways such as volatilisation and leaching.

Fortunately, over the last decade or so, there's been a lot of investment in this space. So we're pretty well off as a country and probably leading in some of the aspects of this due to the previous investment, so $145 million invested over 200 projects Australia wide. There has been a big focus on productivity. A lot of the projects that we've been looking at have not just been looking at the reduction, but there's no point in coming up with a methodology that can reduce all your greenhouse gas emissions if it's not economically viable, so there's been a big influence on productivity.

Australian emission factors and basically refining those emission factors, so when we refer to an emission factor, in the inventory when the Australian Government does its inventory, one of the easiest ways that they can account for, say nitrous oxide emissions is to use what's called an emission factor, and that's just a flat percent rate of how much fertiliser is applied. IPCC states that's at one percent. A lot of the big gains we've made over the last decade is actually realising that, well actually, we're not actually (indistinct 11:39) that much nitrous oxide, we're well below one percent. And in some of those cases we've reduced that (fivefold 11:45) rate for the inventory. On individual farm levels, it doesn't make that much difference.

There's various programs that we've been involved in: National Soil Carbon Program, the National Livestock Methane Program and the National Agriculture and Nitrous Oxide Research Program. And the reason that one's bolded is because that was Peter's – Peter led that one, so that's – these are his slides, so a bit of shameless self-promotion.

What we have here, some of the examples of some of the research that's been heavily involved in this space, because we're interested in the gas coming out of the soil, a lot of it involves actually the sort of chambers and they actually capture the gas in the headspace and allow us to get a really accurate concentration of that nitrous oxide or that methane coming off the soil. It allows us to combine it with other experiments, so this is actually on lysimeters, weighing lysimeters at Griffith in the Riverina. We're looking at water use efficiency or irrigation scheduling and trying to optimise irrigation scheduling to not only increase yields but also to reduce nitrous oxide. And we have various forms of these that we've developed in-house, which stole some technology from the Germans, but they don't mind, so we've now basically done a lot of this work across Australia. I spent my PhD living in that trailer.

As I mentioned, that's allowed us to basically really refine these emission factors and we can basically come up with a map of these high-potential zones where we need to really focus on reducing our nitrous oxide and you can basically see here, nitrous oxide is a function of soil type, climate and nitrogen inputs, so the more nitrogen inputs you have, the greater chance potentially you have of losses.

We've exported our great wealth of knowledge to the world, and that's one of the benefits of having this such strong network here, is that it allows us to also expand to other countries. All these little stars are places where we've managed to get our research into and developed our chambers and sent there for collaborations.

Just in the scheme of things, we basically want to look at how all these things – how important these are in the aspect of things. If we look at a grain crop, we've got this soil carbon sequestration, and when we start to account for the nitrous oxide and methane, we can see we have a pretty big discount. Our total CO2 equivalence, that's what you're going to get paid on as far as a carbon credit goes. We need to basically have our soil carbon minus our nitrous oxide minus our methane emissions. And it's going to be different sources for different industries and so the sugar cane example, we're going to have a lot of nitrous oxide and that's going to give you a pretty fair discount on your carbon.

I mentioned before about emission factors and a lot of the work was about refining emission factors, that's important at an industry level. When it comes to a site specific, farm specific CEA, so you're trying to get this carbon project on this piece of soil, we actually need to be a bit more accurate then. These are averages across the industry. In sugar cane for instance, we can have between one kilogram and 30 kilograms of nitrous oxide lost. If you're doing a CEA, you're doing a carbon plan on that particular soil, we can either be way over-estimating or way under-estimating based on the averages. Based on that, we want to use models, site specific models. We've done this before through the grains industry an APSIM model, and also in dairy. They worked well. As you can see, these are not linear, an emission factor, the fact it's just a flat percentage rate is linear, so we can also have potential to reduce emissions by actually optimising our fertiliser input rates.

There's been leaps and bounds in technologies. These are flux towers, they allow us to pretty accurately get Dan's budget, inputs versus outputs, allow us to look at animal emissions at scale and also nitrous oxide in quite low emitting landscapes and do things cheaply at scale.

Just a summary, non-CO2 emissions are permanent, unlike soil CO2. If we can stop them emitting in the first place, we've done our job. There's an extensive suite of high-resolution data in Australia, so we're really leading the world in our datasets and we have really good models that work with that. But the spatial variability is a major constraint, and that's one of the issues with using an emission factor based system, is that it doesn't take into account that variability. We need to integrate these things with models. I think there'll be a modelling talk later in the session.

I suppose just on that last point, these model-based or carbon methodologies are the norm globally, so the model I presented there before and the dairy systems that's (indistinct 17:06) that's actually used for the greenhouse gas industry in the US, so not only carbon but nitrous oxide and methane, they all take them in together.

I'll just finish on this slide for a plug for the nitrous oxide network. Thank you.

Transcript

Mr Peter Wilson: Our next speaker is Dr Michael Crawford. He's going to provide a summary for the morning sessions. Michael has over 25 years' experience in extension research science management in areas related to soil science farming systems natural resource management. Undertaken a PhD in Soil Science from the University of Adelaide, and through the former CRC of Soil and Land Management. Michael has commenced as the inaugural CEO of the Soil CRC in 2017, and I welcome you to the stage, Michael.

[Applause]

Dr Michael Crawford: Thank you, Peter, and hearing about that, I reflect upon my history, my experience as a soil scientist and picking upon Penny's comments earlier this morning and her long history in this game; it was in the mid '90s as a PhD student under Peter Grace, actually. He took me to a conference in America in Columbus, Ohio. It was called Carbon Sequestration and Soil. The mid '90s, 25 years ago, there was about 100, 150 global experts, soil science experts gathered together, telling each other, "Wouldn't it be a good idea if we could convince people that there might be some opportunities to help offset greenhouse gas emissions by sequestering soil carbon?" 15, 20, 25 years later, the exponential increase in interest has come to the fore.

In my talk, I'm bringing together some of the talks we've heard today, some of the key messages and weaving them into that concept of at the end of the day, it's about the land manager, it's about the farmer, it's about somebody doing something different and reflecting upon the comments that Liz made this morning and her introduction.

In summarising the complexities, considerations (to adoption 02:01); I guess that the key point is that it's not just about the money. It's not just about the measurement. There's a whole range of other things to consider here, too. But I'll also take the opportunity to say a word around the Soil CRC because there's a lot of people who have heard about, don't know so much about it.

Essentially, it's a collaboration of research, industry and farmers working across the country in all states. We've got funding the Australian government for ten years until June 2027, so we're into our fourth year now. It's managed through the Department of Industry, Science, Energy and Resources; just under $40 million from the Australian government, $20 million in cash and another $100 million of in-kind contributions from our participants, our partners, which includes eight universities, four state government agencies, eight industry groups, and importantly, 20 grower groups, 20 farmer groups. And so the key aspect of it is about the researchers and the farmers working together – and that will come through a bit in some of the comments I have later to make – and a focus on delivering research that helps farmers improve soil performance, but more importantly, their productivity and profitability.

To recap upon some of the messages we've heard; first is the benefits of soil organic carbon. Most of the speakers have made reference to this in different ways, and the point I really want to highlight here is that there is a range of benefits from that systems perspective and beyond into the broader landscape systems. That's in addition to potentially offsetting greenhouse gas emissions. There's a whole range of other factors, a whole range of other benefits of soil organic carbon and soil organic matter.

And coming back to this balance thing; that at the end of day increasing soil organic carbon is that what you have in the soil is a balance of inputs and outputs and so it's how those inputs or gains, the additions, less the losses in decomposition. If we're going to get it right, it's just some simple elemental basics in the end, how we can increase the rate of input, and at the same time, decrease the rate of decomposition or loss. If you're to increase the rate of input, and at that same time, increase the rate of decomposition or loss, you're not actually getting too far. I've built upon some of the comments that Dan was making and it make reference of some of the systems we have in the sugarcane growing areas of Queensland, so Ingham. There's systems there where you're producing over a hundred tonnes of biomass each year, but you've also got three metres of rainfall in temperatures above 25 degrees. At the end of the day, the organic carbon level is around 4.5%; not too much different from the wheatbelt of Western Australia.

How do we increase the rate of input? Basically, to bring it all back to this, we can do it in situ or ex situ, in the paddock or bringing our products in. At the end of the day, it's about increasing the net primary productivity. Firstly, removing constraints to production, be it pH, sodicity, low fertility, compaction, whatever. We've heard examples of how that happens.

How we might extend the growing season; so you're getting more inputs over that period of time, having more perennials in the farming system, having cover groups, (double 00:00) cropping, making a situation where your land is producing, growing crops, growing biomass for longer than it might otherwise be.

Increasing diversity in a range of different ways; taking advantage of those niches that might exist in time, both in the seasons that we know about, but also the weather variations over a year, and in place, so the variable soil landscape conditions that we see from a sub-metre to a sub-paddock and beyond type level. And so, different aspects of what people are talking about, doing about it around companion cropping, in the cropping, multispecies pastures, etcetera. And deep-rooted species that help to put carbon deeper into the soil beyond that top ten, twenty, thirty centimetres. And then, ex situ; how we bring carbon in from different ways from outside, be it compost, mulches, biochar, biosolids, manures, etcetera.

One of the other challenges we have in this area is essentially the cost of doing it, making sure it's both agronomically and economically effective, that you're transporting a lot of biomass, and in many cases, a lot of water, to get that into the paddock.

The other side of the balance sheet: decreasing the rate of loss, and (Suze Orgill 06:54) in particular picked up on some of these aspects; reducing tillage and cultivation, retaining stubble, reducing bare soil, maintaining that vegetative cover, that ground cover. In turn, reducing erosion – a loss of carbon that way – and reducing the temperature extremes, and potentially in some cases, in South Australia, Western Australia, increasing the clay content by bringing clay up from deeper in the horizons.

Through the Soil CRC, we've been doing a range of farmer surveys to look at what farmers are currently doing, and a whole range of other aspects; their attitudes to a whole range of aspects associated with soil health and farm management. And we've been looking at some of their practices that they're currently doing. If I was to look at, just for the simplicity of what I call "good practices" and some of those practices I alluded to in the last few slides, in three different areas where we've done surveys so far – North Central Victoria, the Eyre Peninsula, South Australia and the Northern Wheatbelt of Western Australia – the percentage of respondents who said that they are using a minimum or no tillage techniques to establish crops or pastures are up in the 50s and 60s, and depending on what sort of questions you're asking and who you're asking of, you get even higher responses than that.

Those that applied soil ameliorants other than fertiliser or lime, looking at gypsums, organic manures in the last five years are around at 30 or 40%, but variability across the country in these three areas. Those who have sown perennial pastures, it's going to be much dependent on where you are in your farming system and your landscapes. Those who are using time-controlled or rotational grazing, in the 20s or 30s, but potential for improvement there. The key point being that the adoption of many of these practices is variable, but there is room for more, but there are farmers that are doing it already. The uptake will increase where it makes good sense from a farmer perspective, both agronomically and economically.

There are opportunities for increasing soil organic carbon, but not everywhere, and there's also limits to how much carbon can be sequestered in the soil. Again, we've heard through Dan, through (Suze) that soil organic carbon potential is governed, is limited by soil type, texture, climate. In some farming systems, soil organic carbon is reaching its attainable storage limits, so it's not a never-ending story.

The opportunities for sequestration are less in those sandier soils, lower rainfall areas. In many farming systems, we've already had large scale adoption of good farming practices, be it no tillage, stubble retention, crop rotations, soil amelioration, and in many of those cases, also we're seeing that the soil organic carbon levels haven't actually increased all that much, and again, alluding to some of the data that Dan and (Suze) presented there. There's some of the challenges.

Also, increasing soil carbon sequestration may have unintended consequences. I made reference here to the concept of nutrient tie up, as (Suze) spoke about, but in every organic compound, not just (10:17) carbon, but you've got nitrogen and phosphorous, sulphur and potassium, and other nutrients, and that's a two-edged sword. They become the store, the bank upon which you draw upon in the future, but in doing so, you're tying up those nutrients. If yields are to be maintained, this extra fertiliser requirement needs to be factored in somehow.

And if you're growing more pastures, be it going from crop land to pasture, from manual pasture to perennial pasture, or even just improving your pasture productivity, the opportunity is there to potentially graze more livestock. And with more livestock, we're increasing the nitrous oxide and methane emissions as David spoke about in the last presentation. Those emissions need to be considered in a whole of system or a life cycle analysis context.

I want to come back to this concept of practice change, and those with an extension, an experience extension background here, will be well familiar with these concepts about Bennett's Hierarchy, Adoption Hierarchy. There's seven steps, and (we won't go into here 11:20), but again, it's coming back to it's not just a matter paying farmers for extra carbon, but through those seven steps, going through a process where you're putting in the inputs, the resources, the knowledge, you're working with farmers in different ways, you're getting their participation and involvement, you're getting their reactions, their experience, they're seeing what's going on. But critically, you're achieving a change in the KASA, in their knowledge, their attitudes, their skills and their aspirations. When you've got that change in the knowledge, skills, attitudes and aspirations of farmers, that then leads to practice change, and the end results being that social, economic and environmental outcomes.

There's a whole range of issues to consider here; the permanence issue that (Suze) spoke about around droughts, practice change, land ownership change. What happens when those things happen and your carbon's not there, but it was there before? The concept of additionality; I won't go into it too much here, but those (12:20) very much know about this issue, or aren't good farmers doing it anyway? Why pay them extra? The non-CO2 emissions that need to be considers, fertilisers and livestock.

(You see 12:34) a double counting of things (is a looming 12:37) one. Whose carbon is it? If you, as a farmer, are being paid for your carbon by either the government or a corporation somewhere, it's not your carbon anymore. You can't then say, "I'm offsetting my methane emissions through my soil carbon." You can't be claiming carbon neutrality if actually somebody else is claiming those carbon credits at the same time. The time to impact; the time between actually doing something and seeing a result and we'll talk about it more this afternoon. Measurement of carbon to see significant differences are five years plus.

I'll just tell a quick story; working with a senior manager at one of our big supermarkets last year and he's talking about their supply change and how they might work with farmers to be more sustainable or (what can do 13:22) about organic carbon. He said to me – this is a guy coming from our finance and management background, "So what sort of change can we expect to see on a quarterly basis?" and I had to bite my tongue and rephrase the conversation a different way, but, "You're not going to see too much change at all on a quarterly basis. Maybe five years plus." The conversation went a bit dry then.

Measure and verification; I just say that and leave it to this afternoon because there'll be a lot more discussion around measurement and verification this afternoon.

A whole lot of research challenges do remain. Yes, we've done a lot of research and especially on quantifying the state of play, the emissions, etcetera, but when you talk to farmers, what they're still looking for is how we can increase soil organic carbon levels reliably, consistently, profitably, in different farming systems, in different environments and soil types. How do we integrate these practices into our farming systems, around cover crops, around plant diversity, around biological stimulants? There's a lot of discussions in these aspects. How do we actually make it work in our farming system in Australia? How do we manage nutrient tie-up? How we agronomically and economically use external sources of organic carbon?

There's also potentially many win-win-wins here, so it's worth going for. It's good for the soil. It's good for the farmer. It's good for the planet. But it's not just a matter of designing and implementing an effective carbon trading scheme. It's not just a matter of reducing the cost of soil measurement. We also need targeted research to provide farmers with the best ways to sequester carbon, and the best researchers are those who are just half a step behind the best farmers, looking over their shoulder, looking at what they're doing, understanding what they're doing, formulating a hypothesis, testing that hypothesis, extrapolating it to other locations, etcetera. And we also need coordinated, structured adoption activities to give farmers the knowledge and skills, work on their attitudes and aspirations to sequester their carbon.

That's my quick run through, and I'm happy to follow up afterwards. Thank you.

[Applause]

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Adjunct Associate Professor Beverley Henry, Institute for Future Environments, Queensland University of Technology.

Why quantify SOC?

Being able to quantify soil organic carbon (SOC) at the farm/paddock scale is critical to realising the benefits of increasing carbon in soils, including for agricultural productivity, climate change mitigation, climate resilience and rehabilitating degraded land. Each purpose requires a quantification method that is practical and has an acceptable level of uncertainty and appropriate accuracy and credibility.

Why is it so complex?

While techniques to measure carbon concentration in soils for agronomy decisions have been available for many decades, methods have needed to evolve for applications requiring accurate quantification of SOC stock change, including carbon offset markets. Challenges for cost-effective, routine quantification of SOC stock change across a paddock or project area include high spatial and temporal variability, difficulty in measuring changes that are small relative to background stocks, and linking long-term SOC stock change to management when climate and soil factors also strongly influence carbon balance in soils.

Why is quantifying SOC so expensive?

Best practice methods currently involve multiple steps—field sampling, sample processing, laboratory analysis for organic carbon, estimating bulk density—repeated periodically for change calculations. Each step introduces a cost, and an uncertainty that must be managed to ensure the integrity of calculations of SOC stock change and carbon sequestration.

Can the cost of quantifying SOC be reduced in the future?

Newer technologies based on remote sensing, flux measurements and spectroscopy show promise for future practical measurements and, with robust calibration and verification, empirical and process models could support cost-effective, routine quantification of SOC stock change.

Transcript

A/Prof Beverley Henry: Good afternoon everyone. I'm sorry I missed my intro. It's left me a bit flummoxed. I'd like to also thank the National Soil Advocate office for the opportunity to join you this afternoon for the great presentations this morning. I've been asked to speak about why we measure soil carbon and also why it is in practice actually very complex to do. And what I'm going to do is give a fairly general overview, not get into the specifics of individual measurement methods, but to set a context which I think – I hope will give a lead-in to a couple of the talks that follow what I'm talking about. And I'll just also note that when I say measure here, measurement is often used in a broad sense, whether it's a direct measurement, an indirect measurement, a modelling exercise to quantify something, and I'll probably follow that to some extent, and I hope it doesn't get too confusing.

Why do we want to quantify how much carbon is in soil? There's a whole range of priorities, but they can be broadly grouped under three headings: agriculture, other land management, and climate. And these have been spoken about a little bit this morning, but the importance of these for those sectors are very wide-ranging. And while this afternoon I'll be talking specifically about a plot or project scale, a paddock scale for farmers, the priorities that we deal with and the issues that we face in trying to quantify soil carbon cascade across from local to regional to national and international, right up to global initiatives, like the Paris Agreement and meeting the Sustainable Development Goals. Those issues will be on mind too.

And what we're trying to do when we quantify how much carbon is in soil, is to answer a whole range of stakeholder questions. And you've heard some of these this morning, and the questions came up during the panel session about the crunch is, what are we measuring? What can we measure? And what can we give credit for when it comes down to something like carbon credit trading? And that's a question that is starting to hit the ground, I suppose, right at the farmer level. There's farmers who want to go carbon neutral, undertake carbon farming. They have to quantify as well, whether they do it themselves or with an advisor.

The message is that there's a whole range of priorities and scales and questions, and each one needs a method that is fit for purpose. And the quantification priorities that we've talked about have evolved over time. This is a very simplified timeline. Back in the middle of the last century a lot of the questions were about research, understanding soil processes, but also supporting agronomic decisions, including improving fertility with the Green Revolution and all of those issues around food security started coming in. From about the 1990s addressing climate change came to the fore in reasons why we wanted to measure soil carbon, just what was the role of soil carbon as a huge pool of carbon could play in meeting the challenges of addressing climate change.

In the last decade or so there's been an increasing number of papers and discussions around improving soil health, soil health for good land condition or combatting land degradation, for food security and for ecosystem services. And as those priorities have evolved, so have the methods for trying to quantify soil carbon. The earlier measurements were a lot about soil organic matter and then it progressed into understanding carbon and nitrogen stocks around soil fertility and the importance of nitrogen in that context, quantifying the stocks in carbon. Soil carbon as a percentage, the number of grams of carbon in 100 grams of soil gives you the percentage. If you want to convert that to a stock, you have to have a volumetric measure of the soil so that you can go to grams or – or probably tonnes of carbon per hectare. To measure carbon stock change, you have to do that repeatedly to understand the change over time. And you need a certain rigour to be able to make valid comparisons. And that becomes a carbon dioxide flux, removals from the atmosphere for climate change and then there's some modelling and new technology that are becoming increasingly necessary in order to cover some of these priorities.

Firstly, just going back a little bit, the early priorities didn't die, they didn't drop out, they've continued even up until recent decades. The decade from 2007 to 2016, there were about 35,000 papers published on soil organic matter. Most of those mentioned soil fertility as well. But since the 1990s, you can see this exponential growth in publications on carbon sequestration. There's multiple applications for data on soil organic carbon content, stocks and dynamics. And the quantification methods and metrics are developing to align with needs, but that involves a degree of scientific rigour that's needed, so measurement development has to be supported by science, it has to be evidence-based to get a valid measure. If you look at the graph on the top left-hand side of the screen, this is data from a long-term trial at Rothamsted and some of these long-term trials are the most valuable source of understanding the slow turnover of carbon and the processes within carbon that we have. They also provide really valuable data for parameterising models and for building the models that are being increasingly used now in quantification. And picture at the bottom is understanding the global carbon cycle.

Just again, going back to that figure. The blue lines and the red lines are two different sites. They've obviously had different management up to the point of the start of that measurement, and I just want to point out there that the organic carbon stocks are higher in the blue site, I'll call it, and when that happens and you look at the change over time, when you go from a permanent pasture, the solid lines to the dotted lines, so because you're near the threshold of soil carbon content in that soil, you don't get a lot of increase when you continue to have a permanent grassland there. The site in red has a huge increase because it goes from the dotted line, which is a cropping, an arable sign, an arable management, to a permanent pasture, and you get a large increase. You don't have to know only what's happening over time, you have to know your starting point to quantify what you're expected gains are.

Within Australia, we've had large investment in Australian soil carbon research which is supporting a lot of the work that we're hearing about today, the SCaRP program and the National Soil Carbon Program was around from 2009 to 2015 greatly increased the number of soil survey sites that we have across Australia, shown by the dots on the map, and also funded research on spectrometry and other measurement alternatives.

We have lots of science, we have lots of needs, so why is this so complex to do in the paddock? And you've heard this information a little this morning. I'll just go over it though in a very broad context. The amount of carbon stock in soil is a function of the inputs and the losses. And the inputs and the losses are both mediated by a number of variables shown by those triangles, the bow ties, initially predicated on the amount of production you can get, the amount of carbon that can be fixed from the atmosphere into plant material, net primary productivity. And that map looks a bit like Australia's rainfall maps for a reason, and that is because water's limiting in a lot of our systems. But once you get the [plant growth 09:46) the amount that gets in the soil depends on climate soil properties management and the amount that's lost also depends on these variables. And you heard a lot about that this morning, so I won't go into anymore detail except I'd like to show this figure.

This is a collation of data that's been standardised for the three eastern states of Australia and it shows the effect of a number of variables on soil organic carbon stocks. The vertical axis shows the megagrams of carbon per hectare. If you look at the blue bars, aridity is obviously a primary driver. The dryer the conditions, the lower the carbon generally, it drives it down. Clay content, as Fran pointed out this morning, tends to increase carbon if you've got a higher clay content. The three on the right are variables that are most subject to our management as farmers and land management. The thing to note there is that they're very small relative to the others. What we're doing when we try to quantify soil organic carbon is to quantify how much difference we're making relative to all the other influences on soil carbon. And often, if you look on an annual basis, the amount of change that we're trying to measure as a result of practice change may be something like one percent. And that is a challenge for some of our analytical techniques.

Again, to just reiterate why it's challenging, soil organic carbon isn't a water flow, it's not a tree, there's no water flow meter, there's no tape measure that you can put around soil carbon. It's not very visible and it's not uniform. It's not one thing that you can change. The different fractions and the different pools change at different rates and you can't see them change. The challenges for measurement here are that the stocks are highly variable, spatially and temporally and so are the N20s, the nitrous oxide fluxes that David spoke about. And measuring changes in soil organic carbon stock involves quantifying a small change in a large background value. And that's analytically challenging. But it's not all negative.

There is credible science there to support our ability to quantify soil carbon accurately. We can do things. But there isn't yet a cost effective, high-accuracy, one-size-fits-all method or metric that we can apply to measuring carbon credits and making a decision on fertiliser applications. But in the future, for the future, there's promising research and development on new measurement techniques and modelling. There's still limitations, there's still a way to go, but there is a future.

Just to talk about some of the issues we have to consider and what we can do now, managing the trade-offs. This hierarchical diagram, which is fairly simplified, shows that there's often a trade-off between the accuracy and confidence that you can have in a value, and the cost and expertise that you have to put in. That's a reality at the moment. And it's a challenge for farmers trying to do things. It's also a challenge for trying to earn credits for what you're doing if you've got to put in a huge amount of investment to start with.

These methods down the bottom, measuring the percent soil carbon or soil organic matter using laboratory techniques, wet chemistry, etcetera, or dry combustion aren't lacking in value because they're at the bottom of the hierarchy. Several talks this morning mentioned percent carbon. Several of the farmers mentioned it. And they do understand in the large part and know how to make a decision when they know what the percent soil carbon is and how it's changing. It can be used effectively for agronomic decision at relatively low-cost. But having said that, it's important to understand the level of confidence in measurements. Trial, experimental measurements will say the percent carbon will gradually run down under continuous grain cropping. It'll increase if you put in a post-crop. If your soil's low in nitrogen, it will help you build soil carbon. Agronomists can use that information.

This graph though comes with, I suppose a note of caution about understanding what the values are telling you. These are results from an adaptive management grazing trial for either 15 years at site one, the blue one, or for three years. And I thank Dave Rowlings and Peter Grace, my colleagues at QUT for this data. The soil organic carbon in the longer term adaptive management grazing, so an improved management, is slightly higher than in the orange one, if you look at the – you may not be able to see the cross, but the median and the average are fairly close, and it is slightly higher for the long-term treatment.

Unidentified: Beverley, I'm sorry to interrupt, but could you explain what adaptive management grazing is please?

A/Prof Beverley Henry: It's basically managing your stocking to match the pasture. And there are various ways of doing it. I don't know whether Dave would like to add to that for this particular site, but-----

Unidentified: (Indistinct 16:17)

A/Prof Beverley Henry: The thing I wanted to focus on though are the whiskers. This is a box and whisker plot. The vertical lines show the range of values from lowest to highest. While there is a slight difference in the average, it's not statistically significant. And because of that large variability that you get spatially in many of these extensive grazing systems, it's difficult to sample cost-effectively to a sufficient intensity to be able to get a statistically significant difference. We have to bear that in mind. And it becomes important too when we move up this hierarchy.

For quantifying and monetising soil carbon sequestration you need higher accuracy. A fungible commodity such as a carbon offset credit has to have a level of confidence around what it is to have value in a trading situation. There are different challenges, additional challenges for high accuracy and cost-effectiveness. The spatial and temporal variability have to be managed with high sampling intensity. The rate of change of soil organic carbon stocks is often slow and needs longer-term consideration to be able to get a difference, not a quarterly report, it's a dictatorial report on change. And we are still trying to measure a small change on a large background, even over a gap of, say, five years. And the analytical precision then has to also be considered. Quantifying soil organic carbon stock change and carbon credit needs accurate, consistent methods. Standardised sampling or modelling with repeat measures and recordkeeping and reporting and auditing are fundamental to this.

I'd like to just speak very briefly about the Emissions Reduction Fund, not in detail, but to say we've got these challenges about measurement. This is a real example about how those uncertainties in the measurement have been handled in a way that does still maintain the integrity of the carbon credit and gives value to it in a market. The Emissions Reduction Fund soil carbon methods aim to encourage additional adoption of practices that increase soil organic carbon stocks. That's why it was set up. The methods that were developed try to quantify carbon credits that are real, eligible, measurable, conservative and that have integrity. There's the set of legislated Offsets Integrity Standards that aim to support that. The ones in red are those most relevant to what this talk is about, which is measurement, but all must be complied with for a method to be made.

Australia has two soil carbon methods. There's a model method made in 2015 and it looks at estimating sequestration of carbon in soil using default values. It's a fairly restricted method in a way. There's only three eligible activities that were selected because there's more confidence about the change that can be expected. And they use default values from FullCAM, which is Australia's national modelling system that's used in the inventory and it selects conservative soil organic carbon change values to maintain the conservativeness.

The measured method that was made in 2018 is more complex. It has a range of features, and I'm not going to go into all the detail. These that I've selected here are selected for a particular reason. There's a range of eligible activities to encourage more uptake. The next four points there about carbon sampling and carbon analysis are to ensure that the method is measurable and verifiable and that it's conservative. And there are a number of discounts or buffers applied to manage the uncertainty around variability and precision that we can expect. It's widely accepted, both in Australia and internationally, that these methods, particularly the measurement method does have credibility and integrity in the marketplace. There are a number of countries that are looking to copy what's been done here.

I don't have time to go through this whole table. The thing I wanted to note though is that for the various purposes that we have quantification of soil and organic carbon as a priority, for measurement and monitoring, for reporting and for verification, (they do not 22:00) stand alone. They all build on the knowledge that's come from the science back to when all we did was measure soil organic matter for enthusiastic soil carbon scientists and for agronomists and farmers. But they're built on each other. Those data of feeding in, that understanding is feeding into the process modelling that we can do now to verifying remote sensing and flux tower measurements, they are all linked. And I think we do have all of these components now coming together to lead towards a cost-effective routine method for monitoring project scale, but we're not quite there yet.

Just to summarise, soil carbon is quantified for a range of applications, each requiring suitable metrics and level of confidence. The research and monitoring over many decades mean we do have verifiable measurement capability and we have it now, but it comes at a cost and it's not routine. Trade-offs between accuracy and cost need to be understood and appropriate methods used or developed. If we go beyond what is credible, we lose integrity, we lose the value of what we're doing. Analytical, spatial and temporal variability contribute uncertainty to measurement modelling and sensor methods and maintaining integrity in our quantification with acceptable levels of uncertainty is critical for all the priorities that we have, for agricultural productivity and food security, for maintaining and restoring soil health and ecosystem services, for climate change mitigation and adaptation objectives. Measuring soil organic carbon stock change for carbon offsets requires verifiable, evidence-based methods to ensure integrity. We can't move beyond what the science is telling us.

And for the future, we can have practical cost-effective measurements with low bias and acceptable uncertainty, but that will need strategic direct measurements of high-quality that are fit for purpose. We need to fill in some of the gaps in our knowledge. We do need locally calibrated and validated predictive models. In response to the question this morning, I think it was Fran that said we need locally relevant information. And that is what's needed. And we do need to have the capability to learn as we go, so the capability to incorporate farm-level data and remote or proximal sensing data to improve as we go. To share that data is really important. Thank you.

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Associate Professor Brian Wilson, Deputy Associate Dean, Research, University of New England.

What research can we draw from to quantify changes in Soil Carbon?

We can draw from a large body of research to determine what impact management options, land use change and environmental factors have on Soil Organic Carbon (SOC) change. These include extensive scientific literature over several decades; research programs such as the Soil Carbon Research Program (SCaRP) and the Carbon Farming Futures program (rounds 1 and 2 of Filling the Research Gap and Action on the Ground); state-wide soil monitoring programs, national soil monitoring protocols and national modelling programs.

What is the impact of management change on SOC?

A number of management practices have been measured and modelled for their impact in changing SOC levels in the agricultural landscape, including crop rotation management, no-tillage management, pasture management, rotational grazing and using organic inputs over chemical inputs. Overall, the findings show that there is no strong or consistent evidence that management practices led to increases in soil carbon.

What is the impact of changes in land use on SOC?

There are many studies demonstrating significant differences in SOC between land-use types. For example, pasture conversion (i.e. converting cropland to pasture) and establishing native vegetation are two land-use changes that have been shown to significantly increase SOC levels.

What does this mean?

Changes in SOC is largely driven by climate, soil type, land use and then management practices. Climate and soil types will spatially limit where SOC can be stored. While land-use change is likely to have a significant effect on changes in SOC, modification of management practices are likely to result in only modest change.

Transcript

A/Prof Vanessa Wong: Our next speaker is Associate Professor Brian Wilson, who is the Deputy Associate Dean of Research at the University of New England. Brian is a soil scientist and ecologist. He was awarded his PhD in soil science from the University of Reading in the UK in 1992, and since that time has developed a research program in the area of plant and soil interactions. Today, Brian will discuss how much soil carbon can be stored across Australian landscapes, what research we can draw from to quantify those changes in soil carbon, and the impacts of management and land‑use change on soil organic carbon. Thanks Brian.

A/Prof Brian Wilson: Good afternoon everybody. Thanks Vanessa. Thanks for the opportunity to speak. My name is Brian Wilson. As you can see, I'm both with the University of New England, and for my sins, the New South Wales Department of Planning, Industry and Environment. I occupy that strange netherworld between university research and policy, which is a great place to be. I was asked to speak this afternoon, just really about realistic quantities. We've spoken about the theory, the background, the concepts of soil carbon storage. Just really asked to give some examples of realistic quantities of carbon that may, in fact, be stored across the landscapes of Australia.

What I want to do is give you a quick whistle‑stop tour. Think about briefly, just recap I guess, on some of the points that have been made already about the drivers and the status of organic carbon across the continent. Think about some of the constraints on carbon storage, and then think about some of the prospects for future carbon storage across Australia, and some examples specifically from New South Wales. Thinking about options for change. What are the options that actually exist? What are the proven options to increase soil organic carbon? Be it our management practice or land‑use change, and think about the magnitude, and I'll give you hopefully some take‑home messages.

Along the way, I'll be introducing data that I have unashamedly begged, borrowed, and in some cases stolen, from others. All of the data, all the information that I present has been published in the peer‑reviewed literature, so it's all sort of the top end of what we currently know.

Thinking about just recap on the drivers and status, there's been a whole bunch of research taking place to determine the key drivers. We've heard this a number of times already this morning. Regardless of the approach that you take, and I just list some of them here. Decision tree, machine learning, structural equation modelling. All these super‑duper fancy statistical methods have been brought to bear on the huge datasets that we have with regard to soil organic carbon, and every single one of them determines that the number one driver is climate, followed by soil type, followed as a third influence, as a third driver, land‑use. Every piece of research that has been done with huge datasets comes to that same conclusion. Soil organic carbon is driven principally by climate, then by soil type, then by land‑use, in that order.

There are datasets that exists, extensive datasets. There are various state and national models, and I've shown a couple of them here. The data in the top left was Jon Gray from New South Wales, he looked at the whole eastern part of Australia. And of course, we've got the CSIRO soil carbon map. We've got a fairly good idea where the carbon is and what drives carbon, what makes it the way it is.

I'll just put this up to wake you up after lunch, frighten you. Pay attention, I'll be asking questions later. This is just a diagram. It looks very complicated, but I just wanted to make some simple points. This is a series of sites across New South Wales. It covers a rainfall range. You see the shaded bars kind of in the background are rainfall. We have increasing rainfall from the left to the right of the diagram. And you can see that broadly speaking, soil carbon increases with rainfall, particularly when you get to that righthand side of the diagram, and that's where the high rainfall zones are. There's much, much more carbon there. If you then burrow down into the detail of that diagram, you see that for each of those rainfall zones, there's variation in the quantities of carbon. That is driven by soil type, and you can see the little one almost in the middle of the diagram. That is a dermosol, that's a very fertile soil, in the midst of other soils that are not so fertile. Soil type is driving the quantity that can be stored.

And then when you burrow down deeper, you find that in each of those bars, land‑use has an impact even within those little groups. We can demonstrate very, very clearly, and we've got a fairly good handle on where climate and soil type and land‑use actually have an impact on soil carbon. This is just a dataset from New South Wales, but you could repeat that across the continent.

We've got this interaction of series of processes, a series of drivers we know. We know down at the bottom there, climate, rainfall, temperature, vapour pressure deficit, whatever measure used, climate is driving soil carbon. We've then got all the soil type, clay content, drainage, soil constraints, all those issues, the levers, and I think this goes back to what one of the previous speakers spoke about, Suzanne I think, the levers that we have available to us are really land‑use. That's where we can affect the whole process, and ultimately, it's the interaction of all those factors that determines the carbon that we wind up within the soil.

There is extensive scientific literature in this area. We have a lot of information. The previous speaker, I think, spoke of the massive increase in scientific literature in the past couple of decades. We've got a lot of information, we've had a lot of investment through the Soil Carbon Research Program, and the subsequent Filling the Research Gap and Filling the Research Gap 1 and 2. We've got state‑wide monitoring, national soil monitoring protocols, national modelling programs. A huge amount of investment has been thrown at this question. We have a lot of information. And frankly, the people involved in all of those programs are sprinkled through the audience today, so many thanks and apologies if I steal your data inadvertently.

Looking at all of that information, what can we actually achieve? What can we do to store soil carbon? And how much can we store? What I'll do is just do, as I say, a bit of a whistle‑stop around the continent and just give you a few examples of published data. Realistic numbers that have been generated from the research.

And the first one I wanted to look at is work by Fiona Robertson in Victoria, which is related crop rotation management. The question here is management practice. Can we modify management practice to increase soil carbon? In this work, they looked at a range of cropping sites across Victoria, and the various potential cropping rotations that were available. And ultimately, using modelling and various other approaches, they determined that the most likely best bet rotation within our cropping system to store carbon, was canola, followed by wheat, followed by barley, followed by a five-year pasture phase. And remember pasture, that becomes important later.

In the end, using that approach, if we were to apply that approach across the cropping country in Victoria, it would increase soil organic carbon by about 0.3 to 0.9 tonnes per hectare per year. If all of Victoria's farming was converted, and we got, just taking a conservative 50%, you actually achieve 50% of what we predict, that comes to three to four, or thereabouts, megatonnes of CO2 equivalent per year. That's about 3% of Victoria's emissions. It's a number, and it's potentially a big number, but when you set it in the context of the overall state emissions, it's not huge. It's modest.

If we look at tillage management, moving up to Queensland, this is more data that came out of the Soil Carbon Research Program, a series of tillage management sites, we think, and we're often told, that minimum tillage has the potential to store additional carbon by comparison with conventional tillage, because you're not disturbing the soil so much. A whole series of sites across Queensland, no soil organic carbon increase under minimum tillage. That is, no change could be detected. There is a likelihood that if we, and this is a point that I wanted to make, that if we look at data from one year to the other, it is possible that minimum tillage is reducing the rate of loss of carbon, so that you wind up with different numbers from the beginning to the end. But you've got to be very careful about whether that actually means gain, or whether it means reduced rate of loss. In this work, soil type and climate were by far the more important factors, by comparison with minimum tillage.

Let's take another example, cropping rotation, and this comes back to Fran and Dan's work. Looking at over a thousand sample points across WA, one of the key issues, one of the key points that came out of Fran's work particularly, was that there were very significant climatic constraints on where you could store the carbon. Fran touched on this earlier. The dark grey shaded area across the agricultural zone in WA, the area below 450 millimetres rainfall, is constrained. There are significant constraints to the capacity to store carbon. There was a relatively limited storage of carbon in the cropping systems that they examined. But again, one of the points that I'll pick up on shortly, is that there was modest potential to increase carbon under pasture, by comparison with cropping.

In addition, Chris Gazey's work on soil acidity at the bottom, shows subsoil acidity as a constraint to plant growth, and therefore the capacity to store carbon. I guess the point I want to make from this slide, is that there will be parts of the landscape where it is exceptionally difficult to store carbon, simply because of the physical constraints.

Pasture management. We've heard a lot about pasture management. Can we manage pasture systems in a different way, such that we store additional carbon? This is work that I carried out up in the Northern Tablelands, again with the SCaRP program. More than a hundred sites, we compared native pasture with improved pasture. You would intuitively think that if you add legumes and phosphate to a pasture, you increase nutrient, you increase soil carbon. We could detect no difference between those systems, 43.76 as opposed to 43.04 tonnes of carbon per hectare. We couldn't detect the change, and that's what I want to emphasise later, is detection. I think that's really important.

Carbon farming. Annette, I apologise, I'm pinching your data. This was Annette's work under the SCaRP program, looking at two different comparisons. One was cropping, comparison between organic and chemical fertilisers, and the other was grazing rotational versus continuous grazing. I've just circled the numbers, the important numbers, at the top there. There was no detectable difference between organic versus chemical fertiliser, and there was no detectable difference between rotational and continuous grazing. When you look at those numbers, and look on the right under the pasture, rotational grazing has 46.8 tonnes per hectare, when continuous grazing has 40. There's a difference, but it was not detectable. It was not statistically significant. I just wanted to throw that out there, as yet another question, at what point do we have confidence in the data that we're seeing? At what point can we say there was a difference? And that's determined by sample numbers and statistics and all manner of things that we can't go into here.

Just thinking about the Soil Carbon Research Program, this was a huge national program, huge investment. The final conclusions of the Soil Carbon Research Program were number one, there is no strong or consistent evidence that management practices led to increase in soil carbon. Number two, soil type and rainfall are the strongest determinants of soil carbon levels. Third, and probably most significant, soils under perennial pastures tend to have higher soil carbon levels than soils under annual crops, so there was a little taster that actually there are some actions that we believe will increase soil carbon in a detectable way.

That's what I want to talk about now very briefly, is land‑use change, as distinct from modification of management practice. Land‑use change, numerous studies, and I've just given you a couple here, have demonstrated that we can in fact detect differences, significant differences, in soil organic carbon, as a consequence of land‑use change. Changing the land‑use type. The one that's typically held up is conversion of cropping to pasture. And those are the figures that I've shown you here. I don't know how easy it is to read those numbers on the screen above me, but basically continuous cropping, rotational cropping, mixed cropping, 33, 34, 35 tonnes per hectare. Then when you look at pastures, rotational and so we continue, voluntary pasture, introduced pasture, and other pastures, they're at 46 and 44. There seems to be the potential for land‑use change to result in soil organic carbon storage, or increase.

This is an example of work that we've done at our Gunnedah Research Station in New South Wales, where we took an old cropping site, which was previously wheat and sorghum and had been cultivated within an inch of its life, and it had less than 1% organic matter. Into which we introduced a tropical pasture of Rhodes grass, Bambatsi and various other grasses. They produce a massive biomass. They've got huge biomass production, these plants. We've now got a grass cover on what was a bare paddock, cultivated paddock. Over the years, and we've got paddocks 2, 4 and 5, and then I've got an average tacked on the end, the right-hand side of this diagram. Total organic carbon in 2004, 41 tonnes per hectare. We went back and we remeasured in 2017, and we got 70 tonnes per hectare. That is an addition of 2.4 tonnes per hectare per year, on average, of new carbon to that system.

Just as an aside, these were C4 species, so we can use stable isotopes to actually track the new carbon, and that is real new carbon in the system. Another point that I wanted to make very, very briefly from this diagram, is that if you look at the bars, the bars increase fairly steeply in the initial phase, and then they begin to tail off. That could be one of two things. It could be that the new quantity of carbon is beginning to plateau, is beginning to stabilise, or it could simply be that we were in the middle of a drought. The point at which you measure your change in carbon, is determined not only by the nature of the system, and the progressive addition of carbon, but it's also the climate. And we were discussing over lunch, where you take your initial measurement on that climatic variation, makes a huge amount of difference to the quantity that you measure at the end of your action. There are a number of issues in there that, are again throwing questions out and not necessarily giving you answers. But lots of things that we need to think about when we're trying to monetize this commodity that is carbon.

An alternative which has been suggested, whether it can be extensive or not is another question, reestablishment of native vegetation. We know it's happening across the landscape anyway. People are putting environmental plantings in here, there and everywhere. These plantings, again, are at our Gunnedah Research Station. That middle ground is all planted native forest, and we are picking up 2.2 tonnes per hectare per year of additional carbon in those systems, over a 10-year period.

You'll see the diagram at the bottom right. Again, we get a fairly steep increase, and it begins to tail off as we hit drought. Not only are the conditions, the action that you put in place, important, but the climatic conditions, your point that you begin and end within the climatic cycle, but also the historical land‑use. The lower your beginning point, the more likely you are to store carbon. And that was work that Jacqui England and Keryn Paul subsequently followed up on that work.

Just very quickly, this is our New South Wales monitoring program. We've got a range of sites, hundreds of sites now across the state, with cropping, pasture, woodland, across the landscape, and we've got comparative values. Cropping is always lower than pasture, is always lower than woodland. Just that's the way it is.

If we use those numbers, and use the area across the state that is available for these actions, we get a conversion from cropping to pasture, which is probably the most likely of the options available, results in 0.7 megatonnes of CO2 equivalent per year, if we have 10% of the landscape converted. That's a huge, huge conversion rate, and we wind up with 0.7 megatonnes of CO2 stored.

If you then look at the bottom of the slide, the current CO2 equivalent emissions in New South Wales agriculture, just the agricultural sector, is 18.6 megatonnes per annum. That represents, that conversion of 10% of the landscape, would represent, I think it's about 3.5% of the emissions from agriculture alone. It's a significant number, but it's modest.

Take home messages. We know what drives soil organic carbon. Climate, followed by soil type, followed by land‑use. Climate, soil and other constraints will constrain spatially where we can get the best bang for our buck. Equally in high rainfall zones, they may be the best bets. Let's go for the zones that we know have the greatest potential. Change in soil carbon is the key issue. Doesn't matter how much is there, it's about how much it changes. And that's where we get into that question of detection. Modifying management practice, modifying grazing practice or cropping practice. The changes are likely to be modest, and they are difficult to detect with any confidence.

Land‑use change, that is gross change from conversion from one to the other, is likely to be the best bet. But a point I would like to emphasise, and I think we should emphasise more, is that the numbers may not be enormous. But they contribute to the broader jigsaw, they contribute to the larger tapestry. But in addition to that, very, very small changes, increases in soil organic carbon, have huge significance for soil health, and water use and productivity. And we shouldn't lose sight of those. I think we have, in many ways, lost sight of those, with this drive to worry about quantities of carbon.

But finally, huge amounts of information exist on this. There are huge datasets, there's been huge investment. There will be some novel practices that we have not explored fully, and undoubtedly, there are questions that still need to be answered. But it really comes back to that nexus between the huge dataset, the knowledge that we have, and translating that into action. And that's you guys' job.

With that, I'll finish. Thank you.

Transcript

A/Prof Vanessa Wong: Our next speaker is Dr Mark Farrell, who is a Principal Research Scientist at CSIRO. Mark is a biogeochemist with a particular interest in the interactions between organic carbon and nitrogen in soils, and the importance of these on ecosystem function and agricultural productivity. He uses radio and stable isotopes to track fluxes through the soil-plant-microbe interface and spectral techniques, including NMR and MIR, which you'll hear about later, to investigate the chemistry of pools within these systems. Today Mark will discuss how we currently measure soil organic carbon at the paddock scale, what is being measured and accounting for variation across an area and different sampling strategies.

Dr Mark Farrell: Thank you, Vanessa. Thank you everyone and thank you for the invite to speak today. I'm going to be talking about how we actually measure carbon. First of all, I'm going to take a step back. This is probably a slide that in one variation or another you'll have seen at every single presentation today so I won't labour it. Why do we bother measuring soil organic carbon? Well, it's a potential indicator of a decline or improvement in soil condition, as discussed in much of the cases that growers are measuring their carbon. At least traditionally, we were primarily doing it for these purposes. It's a source of nutrients, particularly nitrogen, but it also interacts (01:34) with phosphorous and others. And lastly, and more recently, and the reason most people are here today, is in some way or other, possibly to enable partaking in soil carbon sequestration schemes or similar.

Who quantifies it? Growers and agronomists. I would suggest that they probably quantify 99 per cent of the organic matter in the country. There's a fair number of scientists doing this but it's mostly growers and agronomists doing it on their own properties. Other landholders too, researchers, and one of the questions I was asked to cover was what are the options for citizen science here, so I've put 'Public' with a question, for reasons you'll see as I get through the presentation, how realistic getting that down to a repeatable measurement for stock I'm not (02:23) sure about. Citizen Science. One good example of this is TERN, which whilst it's not citizen science in the traditional sense of the term, they run opportunities for interested members of the public to undertake training and to join them in their field trips, so you're harnessing citizens' interest whilst it's still very much being (02:50), I guess, by researchers.

There are some other things when it comes to soil health proxies. There is the wonderful Tea Bag Index, which came out in, I think, Europe and there's people literally burying tea bags, digging them up a month later and weighing them and submitting the data, and because rooibos and green tea decompose at different rates they've been able to work out that nitrogen tells us something useful. And then one example, you might (laugh now (03:15) that came up, (microblade switches 03:18) by a professor at UWA, he's now at CSIRO, ran a program in Western Australia that had a lot of members of the public merrily wandering around collecting samples, sending them back up to UWA where the analysis was run and people got really interested in which microbes were there.

The reason all these things work well in citizen science is because the equivalent would be if you asked members of the public, gave them the opportunity to go around collect samples and you were only interested in a percent of carbon. We can get numbers on what is provided to the lab very accurately. It is much harder to really make sure that what was provided to the lab is representative of what you're actually trying to estimate is out in the field. Sampling research trends over time, I'm going to present the same graph that Dave did now and, yes, in the last 15 years most of the research in organic matter has most definitely started talking very explicitly about carbon and sequestration, at least in passing, if not being the main focus of that research.

I was hopeful of having another figure from a couple of the agricultural labs as to the changing analysis requests over time, going from a more general soil chemical suite to including carbon. Unfortunately, I've not been able to wrestle that out of them, so that is the only figure I can present on that, but I would imagine that, particularly as we've been talking a lot more about soil health in the last 10 or 15 years and, of course, carbon sequestration directly, I would be astonished if more soil tests weren't being done for soil carbon (microbes 05:00).

Soil organic carbon or soil organic matter? Again, this has been discussed a little bit already. We're all fairly careless in compilating the two from time to time. I certainly am. I probably will do it by mistake in this talk, but soil organic carbon is just the carbon to which nitrogen, oxygen, hydrogen, phosphorus, sulphur, and many other elements are (structured 05:24). Although in modern times at least, it is also actual the thing that's directly measured, and probably get to in a minute, and there are, as (Frank) and Dan and others have discussed this morning, discrete fractions of soil organic carbon that behave as differently as if they might as well be different entities entirely. And there is also the joker in the house of inorganic carbon, which is possibly one area that should be looked at a little bit more.

How do we actually measure it? Older methods. Loss on ignition was, literally, weigh it, set it on fire, weigh it again. Walkley-Black, turn, I think, a brown solution green. It's that long since I did it. It might be a green solution brown. A chemical reaction, basically. A reasonable approximation but it has problems with some of the more recalcitrant forms of carbon that you've heard mentioned already. The current benchmark is high temperature combustion and colloquially called 'Leco,' given the dominant instrument manufacturer. The reproducibility on that is less than 1 per cent error. If you get a representative sample into a Leco instrument that is well run, you will get reproduceable data that can detect these changes. I emphasise again the issue is getting the right sample in the first place.

Moving on from Leco, we have spectroscopy. I know Alex is likely to talk a lot more about this than I will so I'm not going to labour the point too strongly, but one of the big research capacity things that came out of Scarp was really recognising that spectroscopy is a mature technique and now you're looking at a situation where you're processing hundreds of samples a day in the lab on a research-grade instrument like I can see Bruce using there. I'm aware there are other researchers and suppliers in the audience here who are putting a lot of focus into doing this actually in the field, be it hand held or mounted, or mounted on the sensing equipment, as I believe one of the videos will show shortly. I would say that MIR, provided you have the calibration behind MIR it is as good as the calibration data that is coming from the Leco, particularly for bulk carbon. It is reliable, it is easily available and several agricultural labs have these instruments as well as research labs now. The actual measurement, once you've got a sample, is not the problem.

Carbon fractions. I'm going to take a step sideways for a second to go through them in a little bit more detail and come back to them. The reason I brought them in here is because MIR is a tool that has made measurements of these on a grand scale feasible. You have the plant residues and (surface 08:18) isn't buried, which we don't really count as soil at all because we typically presume that they go in (08:24) so quickly. They actually add noise to the underlying signal that you're trying to measure. You have particulate organic carbon and you have the humus-like organic carbon. Those two are in the soil and they form this continuum vertically from the really fresh to the highly decomposed. Loss of carbohydrates, a decrease in carbon-to-nitrogen ratio as a lot of the carbon gets lost as CO2, whereas the nutrients remain and become more resistant to decomposition.

The final fraction which I deliberately left off (at this stage 08:58) and will introduce now, is the resistant carbon, the charcoal-like carbon, which is quite different, but we presume mostly formed through fire and soot, and it has a residence time in soil in the tens of thousands of years that you're hearing about, but it isn't typically formed in the same way as the rest of it and it certainly doesn't provide the same function. And they look quite different as well. I hadn't anticipated just how small the screens were going to be in here when I put this on the slide but there's the particulate carbon when isolated. When you look at it under a microscope, it still looks identical, identifiable part (of plants 09:38).

The humus-like carbon, the one in the middle, that looks much more waxy and gloopy, and that's because it's mostly dead microbes, and one of the reasons it's there is because it's bound to (09:51) to protect the aggregates, as other speakers have said this morning. It's not actually that chemical (09:59) itself, or most of it isn't, it's just protected from decomposition. One of the presumptions as to why perhaps tillage had been seen to be so destructive to organic carbon stocks. If it was actually the real chemical recalcitrant, turning (it upside down with a 10:15) wouldn't have that much of an effect on it. The fact that it actually isn't a chemical recalcitrant and is protected from being decomposed is what keeps it there and one of the reasons that tillage was always seen as such a bad thing for it. (Dare I say, like I say 10:28), they're more charcoal-like. And chemically those three fractions look quite different. These are (10:33) spectra. I don't want you to look at them in any great detail other than to see that particulate and the humus-like are different but, sort of, of the same order, whereas the resistant, the charcoal-like, is a very different beast indeed.

That's the fractions. It's definitely worth measuring them because here are six samples from Scarp. This is another one of (Jeff's) figures, and those are carbon content for those, so it doesn't really tell you anything other than that some are higher than others. You've got no information about how vulnerable that carbon might be. You've got no information about what other services it might be providing. Once you have the fractions, you can start seeing quite quickly that there are differences there. For the one on the left with that really large green part there, (for some it's 11:19) on the right, that has an awful lot of – in fact, about 50 per cent of it is a POC. The more fresh material is also the more vulnerable material. The one that has the highest carbon stock, if you change from the practice – from the land use that had put that there and say you went from pasture to cropping would be an example of the (drawn brown 11:39) stalk. You might expect a lot of the green bar to go very quickly and all of a sudden it wouldn't be able to have the highest concentration amongst this lot. On the other hand this one, is actually mostly fairly-resistant to carbon (11:53) in the resistant carbon.

One of the things that (Jeff) did, and the map that was put up earlier, one with Rafael who we see over there, and we come up with the idea that we can actually have a vulnerability to change metric out of this and the more POCs the more vulnerable you are, but you basically get a number that is useable, we can put these things into a model. Why should we bother? Well, fractions (12:18) an awful lot more than just carbon itself and going back to how we measure things, MIR for fractions is pretty prudent, well written up, peer-reviewed research, this can be done now and because you would have exactly the same analysis from it, you have the database underlying it, as it is to use MIR to measure just bulk carbon. It costs you no more, provided you have the database behind it. The trick is having the database behind it. But we really should bother when it comes to modelling because we're never ever going to be able to measure across the country at the rate required to actually monetise this. We need robust models that can do a lot of the heavy lifting for us and basically cheat us out of having to measure quite as much, and having the fractions allows you to build much more robust models and, indeed, the fractions I've described above are actually what underpins this whole carbon (part of FullCAM 13:13).

As I said when I stood up here, in some regards I actually (got a box 13:23) and that's the easy bit. We can do that. It's mature technology. Once you've got a sample for the lab you can get a repeatable number if the lab is doing its job right. Your problem is getting the sample from the best place, and that is what makes (13:35) citizen science, I think, problematic for this approach because it takes great care to get a sample that you can really turn into a stalk rather than just being a percent of carbon. And one of the reasons is these stalk bulk density and you basically have to turn the carbon percentage into a stalk. You have these five different lines on the table, five different rows on the table behind me. You've got the carbon concentration, you've got the water content of the soil, the depth the soil was taken, which then gets you to a bulk density, and then you've got to subtract any gravel that was in there, and that eventually gets you a carbon stock at the end.

What you see here, this is an example that (Jeff) has knocked up. There's pretty much a 10 per cent error between what is actually in the soil versus what we've been able to observe, but most of that error is coming from things that are not in the lab, it's coming from having got the sample in the field. Everyone's like you actually dug 30.2 centimetres rather than 30 centimetres, so a 2 millimetre difference, but you multiply that across the whole of the paddock, the error's there, it's not (14:46).

And then there is equivalent mass, which is the other method and, indeed, the one that is in one of the methodologies, and the reason equivalent mass has been seen to be looked at is because, well, certainly some of our soils, Vertosols, for instance, shrink and swell and change their bulk density quite naturally. If we weren't considering equivalent mass, simply driving your heavy truck over it would give you an apparent increase in soil carbon stock because you'd have included this bit, you dug lower down than you did before and you've physical got more soil in there and you have squeezed the air and water out of it. Actually, perversely, increasing organic matter normally comes with a decrease in bulk density. (15:32) improved the structure, it made it more friable, so you'd actually underestimate your carbon stocks. This is why equivalent mass been put forward as the way forward because you do it on the basis of an equivalent mass of soil taken rather than trying to fix it to that volume.

Does this matter? Well, yes, it does. This is from one of the (15:56) research projects that (Jeff) led with Brian, I think, and a few of us on temporal variability, and this is Narrabri, so we're talking (16:02) versus (old), and you can see the red, the equivalent soil mass stocks there, there's much less variability about them and it's a much more consistent, albeit slight, trend rather than the much noisier blue dots which are exactly the same (16:16) measurement, the same Leco measurement done on both of these but calculated differently.

On to sampling strategies and how you'd actually get the soil in the first place. We've gone back from the digging the hole, and that's fine. Where do you actually dig it? With no prior information at all you might go on a random way and just go about your paddock, but the trouble is you're missing points. The top left and bottom right, you have no information about stock. So if you have no prior information at all it's probably a good idea to take a gridded approach so you're (at least getting some land 16:50) coverage and you might want to do – how much effort you want to put into it and what samples you take, but that's not really that realistic because we will always have some knowledge of spatial variability and if we're talking cropping, it'll be coming from a yield monitor (on the header 17:08). There's remote sensing data. There are freely available soil (weighs 17:13). We'll have some idea that the paddock isn't actually this homogenous plot of land, it is actually quite variable beneath, and landholders will know where their non-productive areas are. You then structure your sampling around that so you capture that variability and that helps shrink those (errors out 17:31) because you actually got three effective information areas rather than trying to treat it as one. You're treating them as three different entities and then (summing) them together at the end, rather than bringing all that variability to ones which gets you those huge error (17:42) that we've been talking about, and that's the difference between being able to observe a difference and actually being a difference. There might actually be a difference, but depending on your (17:51) structure you're just not able to observe. And there are pathways forward to help growers and practitioners work their way through this, how you might want to go about developing something (18:02). I'm not going to go into that.

Some very simple conclusions I want to give. The measurement of soil organic carbon concentration itself is highly accurate, highly routine and incredibly high throughput, particularly with automated (infrared 18:16). That's not your problem. Fractions are really on the cusp of being operationalizable and because we use the same technology it costs a lot more to get the data that fills those calibrations but it's not orders of like – the eventual cost, you're not sort of adding a zero to the end of your analysis cost. Your real problems are getting a proper handle on the spatial heterogeneity, which will always be a big problem with - you have the gold standard analysis in the lab, but you need to have got the perfect sample to the lab to get the gold standard number at the end.

I'm just taking quarter of a mil as an example from that table I showed earlier of (Jeff's) data. If you were sampling yearly you'd need to detect about that hundred tonnes of carbon per hectare, you'd need something like – they'll detect just a change of 370 kilograms, I think, the difference. That's tiny. Getting the variability that will stop you from being able to do that is in how you get the sample in the first place, not in the lab.

Thank you very much.

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, delivered by Professor Alex McBratney, Director - Sydney Institute of Agriculture and Professor of Digital Agriculture and Soil Science, The University of Sydney.

Estimating SOC at the paddock scale

In any soil-carbon-for-climate-mitigation project there is a need to audit the change in solid-state soil carbon over a specified land area to a fixed depth over some specified time period.

In order to count carbon change it is necessary to audit it twice, at the beginning and at the end of the specified period. Auditing of the total amount consists of two main aspects (a) sampling design, (b) measurement technique. Soil carbon shows a fair amount of natural variation in any land area so probability sampling is required to deal with this variation and to obtain realistic estimates of uncertainty. Some kind of stratified random sampling is generally preferred.

Differences in SOC estimation methods

Measurement may be direct or indirect. Carbon stocks generally require two measurements: the carbon concentration and the soil (bulk) density. Direct laboratory and field methods have been devised for both. Lab methods are more precise than field methods but the former are much more expensive. It is likely that field methods are more efficient for a given level of auditing (= sampling and measurement) investment. Indirect methods which include process modelling and remote sensing can give an indirect estimate of carbon change but are more likely to be much less certain but may be less expensive. The cost v uncertainty trade-off for these methods is currently unknown.

Confidence levels of estimating SOC

The uncertainty of the carbon stock change should be estimated formally and used to discount the amount of carbon stock change recognised which in turn will incentivise increased sampling. Statements of cost per hectare for soil carbon stock change auditing only make sense if they are accompanied by a statement of the uncertainty required.

Transcript

A/Prof Vanessa Wong: Our next speaker is Professor Alex McBratney, who's the Director of the Sydney Institute of Agriculture, a Professor of Digital Agriculture and Soil Science, and he's based at the University of Sydney. Alex holds a Bachelor of Science, PhD and Doctor of Science Degrees in soil science from the University of Aberdeen in Scotland, and the Doctor of Science Degree from the University of Sydney for research in precision agriculture. Alex has made major contributions to soil science and agriculture through the development of the concepts of pedometrics, digital soil mapping and precision agriculture. Today, Alex will discuss estimating soil organic carbon, the differences in soil organic carbon estimation methods and the confidence levels of these methods.

[Applause]

Prof Alex McBratney: Afternoon everybody. Great to be here. Thank you, National Soils Advocate and team, for inviting me. It was a great surprise, but here I am. I think Bev gave the context for my talk. I think Brain – well, Brain, what can I say? His talk was so mellifluous, I'm going to try to emulate the way he spoke and not as well obviously. And Mark, of course, he actually did give my talk so it's very easy for me now. The CSIRO are always there just before we are. That's how it works, hey, apparently.

Anyway, look, we've been working on this for a long time, on trying to measure soil carbon, soil carbon change, because around 2008, when the Australian government first started to think about soil carbon as a way of offsetting atmospheric CO2, a lot of soil scientists, or my colleagues, were saying, "We won't be able to do it because it's too difficult to measure. It's too hard to measure." And I thought, "That can't be right. That cannot be right. We must be able to do something." We did a lot of work from 2008 until about 2012, and then of course, governments changed their attitudes and we've lost about eight to ten years in this game, where nothing happened, and now we're back at it again. And I'm glad we're back at it because it's a huge opportunity, I think, for the country, to be able to do this, and if we – like many things in soils, we are probably ahead of the world in this, in our thoughts and our ideas, and we just have to believe in ourselves and actually get on with it.

Now, figure out how to work the technology, Alex. Background, oh, there you go. I think the two questions around soil carbon sequestration for climate change mitigation are simply these, simply put: how to put more carbon into soil and keep it there, and how to demonstrate that that has been done. That's the measurement reporting verification part. Luckily, I'm not talking about the first part because that's the hard one. I'm just talking about the simple one which is the second one today, and mainly we've heard about the methods that we can use to do that, so maybe you can see my talk is a bit of revision and trying to put some ideas together.

Before we do that, I had this filler slide which is just in between sections, but I noticed that various other speakers today had advertorial slides, so I thought, "Well, I'd better make an advertorial story out of this slide." My advertorial about this slide is this is a research station at Narrabri in New South Wales, University of Sydney Research Station. This is its Diamond Jubilee. It's been there since 1961, and we've been working on it all the time since then, and I heard some interesting comments from the government last week about Sandstone Universities and what they could do in agriculture, so I'd just like to say that the sandstone university that I come from – and I'm sure many others – have a large part to play in the ag sector and the future of the ag sector of Australia, and we interact intimately with the rural communities in these areas. That's all I wanted to say about that aspect.

This is real. This (petroglyph 05:08) – that's its official title. This (petroglyph 05:11) was made a couple of years ago for the World Soil Day to celebrate that, on our research station. These are the vertosols that Mark was just talking about. Now, on this research station, which is largely for plant breeding, wheat breeding, it's been cultivated continuously for about sixty years, so it's lost half its carbon. The soil, if you take some of the soil and stick it in some water, it dissolves immediately. It's a heavy vertosol, 70% clay. At the moment, we're busy trying to figure out how to put the carbon back through zero till because traditionally we just tilled it every year. But now we are doing zero till and cover cropping. There is a carbon story about that.

A little bit more about soil carbon, a bit of revision: putting carbon into soil is beneficial to the soil, to the climate, the ecosystem and agricultural productivity. I think we'll all agree about that, and the main reason why the soil scientists are here is because of that. It's not just about the climate change thing. It's not just about the monetisation. It's actually about all of those benefits and core benefits.

I think what we need to say is that in the field, when you go out there in the landscape, carbon is quite variable across the landscape. It varies quite a lot. But that variation does have a pattern to it, and we have to understand that, and we have to understand the variation in paddocks across farms, across catchments. And understanding that variation will help us with the sequestration management options – where should we do certain operations to try and increase carbon – and also with measurement; what's the important places to measure in this landscape?

And the last one which is possibly obvious, but worth repeating is that the bigger the area, the larger the variation, and the more observations of carbon are required. But it's not linear-related to the area, and I'll show that in a minute, so just a few slides.

This is some of their work using the Google Earth engine. We can predict, make estimates of how much carbon there is everywhere in the world, and this is at a resolution of 250 metres, so every 250 metres, we've predicted how much carbon there is. I think the main point here is there's a lot less carbon in Australia then there is in some other parts of the world, but there is a discernible pattern, and as has been said, it's largely related to climate, but not totally. It's also related to topography and some of the underlying geology or meteorology. That's useful to know, that everywhere in the world we can at least now make an estimate of how much carbon we think should be there. That helps us in our work.

If we go up to North West New South Wales, Narrabri, Gunnedah, Liverpool Plains, etcetera, this is a map of the carbon there and you can see across that landscape, it's varying from 20 tonnes per hectare to 125 tonnes per hectare to the top 30 centimetres. That's work that's from the Soil and Landscape Grid of Australia which a number of people in this room have worked on, and we're working on again now to improve this mapping. But it's a good basis for work around sampling and monitoring of soil carbon, so that's important work.

These lines are based on real data, but roughly speaking, the amount of variation of carbon varies with (a log 09:21) of the area, which is very commonly known in ecology, that that relationship happens. What does that say? I think it largely says that once you get to a certain area, it doesn't increase that much, so it might be better to monitor bigger areas rather than smaller ones, to get more efficiency in monitoring and measurement, and I'll come back to that point.

Auditing soil carbon changes, which is the way I frame this because that's what I've been trying to do; all the time, I've been trying to come up with an auditing method that would come between the producer of the carbon and those who are buying or aggregating the carbon. Roughly how you might do that: measure the total amount of soil carbon and its uncertainty, at some time, t1 and measuring it again at some time t2, and being a soil scientist, I think t2 minus t1 needs to be about five years. It could be ten years, but as we've heard today, if it's one year, it's not quite long enough to get a good estimate of the change.

The change is the carbon at t2 minus t1, which you hope is positive. It's not necessarily positive, but you hope it is, and that's the amount that you're interested in. But you also have to be interested in the uncertainty of that carbon content which we've heard about. And the thing is, the uncertainty is not – you don't take the difference there. You actually add the uncertainty at the two time periods, so that's important. I think the thing to say here is if you want to get at that uncertainty – and I'll show you how you use that later – you need some formal sampling strategy to get that uncertainty formally, and stratified random sampling is a good way of doing that.

This would be a farm on the Liverpool Plains, a couple of thousand hectares, and the different colours are the different strata and then you would put various samples in each one of those strata. These strata are made from estimates of carbon.

Now, I'm going to suggest to you that there are four main measurement methods, "measurement" in inverted commas, but to do this, so one would be stratified random sampling under lab measurement, which we've heard about from Mark. Another one would be stratified random sampling under field measurement. But because the field measurement isn't as accurate as the lab method – and I'll show that in a minute – you need to do some calibration sampling to at least find out what the uncertainty of the field measurement is, and then there might be some indirect measurements, remote sensing being one that's often touted. That's just basically an empirical model which relates the carbon to something you can see in the remote sensing. But that also needs some calibration sampling and lab measurement, so there's a bit more work needed there. And the last one would be – which we saw the process modelling which I call soil carbon turnover modelling, which also requires some calibration sampling and lab measurement. These are four methods that I think are valid and can be compared if you estimate the uncertainty. With out the uncertainty, we know nothing about these or how they perform.

Measurement, as has just been said, is of soil carbon stock, so that's the mass of carbon divided by the volume of soil, so it does require measurement of soil carbon concentration and soil dry bulk density. And as we heard, generally speaking, the bulk density is more variable, more difficult to measure than the carbon concentration.

If we look at how that works out for these methods, lab, we might do the LECO or as a standard – these are examples – or bulk density by gravimetric method, just weighing a fixed volume. In the field, we use infrared spectroscopy; largely near-infrared but it could be mid-infrared or there are other techniques like inelastic neutron scattering that could be used for this. Bulk density can't be measured by gamma densitometry, so there are ways of doing it in the field.

Remote sensing; well you could look at various parts of the spectrum, the electromagnetic spectrum, but for example, reflectance of the soil surface, if you can see it, doesn't necessarily give you any direct estimate of bulk density. That's one of the drawbacks of remote sensing. But there are numerous modes of remote sensing that might be used, and I don't have time to go through all of that. And in the process modelling, it's just basically a kinetic pool model that Mark talked about. The clever thing about that is it does work on the stocks itself, magically deals with that change in volume in some process ways that I don't understand. It's magic.

Measurement; and then you have to come to, "Well, how precise or accurate are these things, and how much do they cost?" because that's what really matters, and I think for lab measurements, about 5% accurate per site, per observation, and if the relative cost of that is one unit, and that might be a hundred dollars, the field method might be 15% and the relative cost of that would be about a third. Now, it's very hard to put numbers on the remote sensing and the process modelling, and that hasn't really bee done. I've seen very little work on – or no scientific work – hardly any at least – on quantifying either the uncertainty or the relative cost of these, and that's the big unknown in all of this. But I'm suggesting 50% as a guess for these two and I'm being – probably the relative cost could be less than what I'm suggesting for these two, but I just put them there because – but this is the unknown. That's an unknown in all of this stuff, because if we want to bring in remote sensing and process modelling, we really need hard and fast numbers for those. That's the research that's needed in this space. We really don't know the cost per unit area versus uncertainty, so that's an unknown

This is that farm Nowley, which is in the Liverpool Plains, which is also one of the Sandstone Universities out there trying to do agriculture and talk to the community. The carbon stocks; so even on this farm, the carbon stock can vary a great deal, a huge range, and that's something to be understood. It can vary a lot across a whole farm. A couple of thousand hectares here, and that's the uncertainty of the estimate of the stock, and when we do the fancy stratification, we use both of these numbers to do the stratification. And that's how you stratify and that's where you'd take the samples, so that's just an example of how you'd do it. I won't go into the statistics of all of that.

This is some of our work that we're doing at the moment on field measurement. We've been investigating NIR in the field and basically pushing a probe down into about a metre, and every one of those little blue dots is actually a measurement. It makes many hundreds of measurements as we go down so we can get a very detailed picture of carbon and if we want to measure at any particular depth range, then we can get an estimate of the average or the total for that depth range.

And go to Mark's point about the equivalent soil mass, which is really a Lagrange coordinate system, I think. I think it really needs to be better expressed. We can actually do that using this method because of the way it works. We can estimate the equivalent mass of soil from the – because using the NIR, you can also estimate the clay and sand content so you can do that, and calibrate that. There's an advantage in doing this in the field. In the end, this method might be as accurate as actually taking a sample back to the lab, but that remains to be seen. We wouldn't claim that at this point in time.

Using those numbers in the previous table, if we look at the relative sample densities that you need for the two methods – and all these points in here are different fields. Actually, these fields are in the US because I should say all this work that we're doing is funded by the US Department of Energy, not the Australian one, the US Department of Energy, unfortunately. But glad of the money though. You can see that the field method NIR has a higher sampling density, but when you look at the relative – the sampling density is about twice as much, but remember the cost is only a third, so you're ahead using the field method, and that's what you find when you do this stuff.

And a cautionary tale – no, I don't think so. Just about how to use the uncertainty; so I argue all the time. Last year, the government was saying, "We've got to get the cost of this down to less than $3 a hectare." Well that's a nice ambition, but with $3 a hectare, what uncertainty goes along with that? And if you don't specify that, you can't get there. The cost per hectare is an incoherent concept without considering the uncertainty, but uncertainty can be used to discount the amount of carbon sequestered and payments, so your credit based on the uncertainty. It's a risk-based approach.

Let's imagine that we had some method that – we had a field and we found that we've got a thousand units of carbon, okay, a thousand tonnes, and the uncertainty of Method A is 5% and Method B is 30%. If you discount it using a normal distribution – so that's where the Z score comes from – the uncertainty of the stock difference here is 50 and then the other one's 300, then the Z value gives you those numbers. The amount that would actually be credited under Method A would be 918 tonnes, and under Method B, 506 tonnes, and that's how you can use the uncertainty in all of these methods. And if we're developing new methods, we should observe that principle, I believe.

I think each of the four methods should have a formalised methodology. It looks like a couple of them have some kind of formalised methodology, but they can be improved. And any acceptable methodology requires a formalised measurable uncertainty.

I haven't covered the standard methods. I haven't covered the fancy ways we have of constructing these strata, which we invented a long time ago, and I haven't covered the forms of carbon. But really, inorganic carbon, which is carbonates, has to count as well in this because we could be gaining carbon on the surface in an irrigation situation, and losing carbonates at depth, which is what happens in a lot of the irrigation areas.

Conclusions; how to put more carbon in the soil and keep it there? Well, I'd still say to everybody who walks away today, "That's the biggest issue. That's the one that needs the most work. That's the one that needs investment." How do demonstrate that has been done. This the measurement thing that I've been talking about.

There's a few key questions remaining there, but we're well on the way to solving that, and I would say Australia's leading the world on that. This is a quotation from – who wrote that? Anybody remember?

Audience Member: (23:02).

Prof Alex McBratney: Winston Churchill, and I'm very much an optimistic and we should get as much carbon into the soil as we can because, as somebody said today, we've lost about a third to half of the carbon that we had 200 years ago, and we should try and put some of that back. And the fact that it was there lets me think that we can actually put some of it back. Okay, thanks very much.

Summary

This is a summary of the presentation given to the Forum, provided by Dr Senani Karunaratne, CSIRO Agriculture and Food.

Why do we need soil organic carbon models?

Models are typically used to predict/simulate soil organic carbon (SOC) stock or stock change over time with response to different land management practices and climatic conditions. Generally, approaches used for modelling SOC can be categorised as; empirical (data driven e.g. statistical or machine learning) or as mechanistic models where work presented here is focused on the later approach. There are more than 250 models being used to simulate SOC worldwide. The mechanistic models are used to track the movement of carbon in soils due to ecosystem processes largely driven by interactions between soil microorganisms, climate, other soil properties and human induced management changes.

Modelling is the only viable option to present a baseline of what would have occurred if there is no management change. Modelling can also reduce the cost of measuring SOC by providing accurate estimates at different spatial and temporal scales compared to other SOC measurement technologies. Advances in characterising the composition of SOC has resulted in the recognition of measurable SOC fractions with different turnover times. Multi-pool models such as FullCAM/RothC can effectively model the dynamics of SOC stored in these fractions

National vs. project scale modelling

National scale soil carbon models draw on multiple data sets such as climate, land management and soil databases. In Australia, the FullCAM model is used to track the terrestrial carbon pools including SOC across the continent which underpins the National Greenhouse Gas Inventory. Additionally, model outputs have potential to provide valuable information for setting up SOC monitoring networks, provide insight into environmental drivers that determine the distribution of SOC across the nation and its diverse bioregions, provide insight into national scale SOC sequestration potential and vulnerability of the current SOC stocks. However, national scale modelling represents the average behaviour of the dynamics of soil carbon. Compared to national scale, project level modelling requires customisation of model inputs, initialisation and parameters.

Model validation and quantification of modelling uncertainties at both national and project scale are important to provide realistic model estimates. If a model is used for carbon sequestration projects, such validation and quantification of model uncertainties will reduce the risk of over- or under- crediting such projects. Project scale SOC modelling can help to improve national scale models through filling gaps in the national datasets.

Next-generation soil carbon models

Combining data streams, the integration of geospatial datasets with process-based models may predict or simulate changes in SOC in near real-time. Additionally, incorporation of uncertainty analysis toolbox with such models will enhance the quantity of the simulated datasets and the credibility of the results.

Transcript

A/Prof Vanessa Wong: Our next speaker is Dr Senani Karunaratne, who is a Senior Research Scientist at CSIRO. His research focuses on measuring, modelling and predicting variation present in environmentally important properties in space and time. Prior to joining CSIRO, he worked as a Senior Research Scientist for Agriculture Victoria and co-led research activities on the development of new methodologies for the use of next generation sensor technologies in pasture agronomy research to enhance the productivity of Australian dairy production systems. Today, Senani will discuss temporal modelling of soil carbon, why we need models, the national versus the project scale modelling and the next generation of soil carbon models.

Dr Senani Karunaratne: Thank you NSA and thank you, Sue, for inviting me. My presentation is on temporal modelling of soil organic carbon. The key take home messages from my presentation is that selecting appropriate carbon models depends on the requirements of the project. It can be a national scale and it can be based on the project scale. And also, the model inputs, that's the initialisation approach, use of appropriate model parameters are key to get realistic model output. And also, as some of the previous speakers mentioned, like quantification of model uncertainties and validation of the simulated results is important when you carry out modelling.

When you look at different methods of measuring, of predicting soil organic carbon, there are different methods. And one of the common methods is direct measurement and then a proximal sensing and the remote sensing, and we have computer models. Now, representation in terms of accuracy, direct measurement is the gold standard that we use because those direct measurements are used for calibration of other methods. Now, when you (talk 02:22) about the spatial representation, use of remote sensing with the direct measurement data can represent large spatial landscapes. When you look at the computer models, I put it in between proximal sensing and remote sensing, depending on how we parameterise, how we determine the inputs (indistinct 02:40) models of the accuracy of the process-based models can be varied. It's important to consider those aspects when you're deciding policies and also selecting an appropriate model.

Now, this has been discussed throughout this forum, so I'm not going to go through it again. It's all about balance between carbon input and what's been lost from soil. There's quite a bit of discussion on this, so I can skip this slide.

In terms of modelling, what we're trying to do is actually try to represent this complex real world of carbon flow from plants to debris to litter to soils through a computer model, so we made a lot of assumptions. We can't realistically represent what's happening in the landscape as it is in the computer. We had to make some assumptions. And what's important is that we tried to track carbon from different components to go into soil and within the soil itself, we also tried to track this carbon. There are different circles in red and yellow colour. These are like the addition of carbon to the system and loss of carbon. Now, within a model, we make assumptions that (indistinct 03:56) and we make some (levers 04:00) to move carbon from one (component 04:02) to another (component (04:03), so that's how we represent the carbon cycle within a model.

Now, this slide also has been discussed in detail. But I just thought of showing this because it's important to understand that soil organic carbon has like different components. Knowing this composition of carbon is important when you try to characterise or run models. There are model – different single carbon (indistinct 04:29) models, but most of the models that I'm going to discuss is like multi-compartment. Having the composition of the carbon itself is important to initialisation and also to calibrate these models.

Why we need models and how we can classify these models. When you talk about the cost reduction, a model is one alternative that we can use to predict or simulate carbon, so it can be used as a tool to reduce the cost of sampling over the time. And modelling is the only viable option that will present a baseline of what would happen if there is no management change. Obviously, we can have, like (indistinct 05:11) experiments, but that's required money and then time to conduct these experiments. However, models can be used as like a proxy to see what's going to happen. And also, the models can be used for the assessment of the vulnerability of a carbon project in future. Once we know the composition of the carbon, we can use that composition to direct how vulnerable these carbon projects in future climatic conditions.

Now, there are more than 250 models. I'm not going to talk about all these models. But my focus will mainly focus on taking more examples from Rothamsted carbon model and FullCAM carbon model. And there is a great tendency now, more recently to use this model in spatial context rather than running a model in a point. We try to run the model in a more landscape scale, considering different spatial inputs, I'll go through much later.

Classification of the models. Broadly, any carbon model or any soil model actually can be classified as mechanistic or empirical. That doesn't mean that a mechanistic model is not using data, it's actually using data to construct the model, but this is the basic classification. And this particular talk mainly concentrates on mechanistic models. Mechanistic models based on the structure of the model can be classified into four main components. There are different classifications, and the current – this particular talk is mainly going to focus on process-based multi-compartment models.

To give you a quick idea about process-based modelling, though it looks like a black box, it has some sort of understanding about the dynamics of carbon in the landscape scale. I have taken example from FullCAM, which actually underpins the Rothamsted carbon model within the FullCAM model. FullCAM is a collection of different model and it's an acronym and used for the National Greenhouse Gas accounting. The Rothamsted carbon model, there are five pools that represent different elements of carbon within a composition of carbon. And these pools can be classified as active and passive. The (indistinct 07:27) pool is a passive pool, not subject to cycling.

And out of these four different active pools, they have their own characterisation rate of decomposition governed by temperature, moisture and cover. And this happens using a first-order decay process, so if you have like a one carbon (SOC 07:50) in a particular month, then what will be the result in the next month is a function of its own rate constant and the temperature, cover and moisture. And because we are running this model on monthly time steps, we divide by 12, the rate constant to get a – because rate constant is given on an annual basis. That's the scientific basis for background of a process-based model.

It's important to consider that these process-based models also impact (indistinct 08:28) using datasets, especially the long-term trial datasets. For FullCAM model, we are using 104 sites scattered in major cropping regions across the country to calibrate the model. For example, using this temporal long-term trial data collected quite a long time ago, some of those datasets, we have been using the measurable carbon fractions and the model-simulated carbon data to fine tune some of the parameters and try to match these measurable carbon fractions. Having this type of optimisation with the measured datasets in modelling is important because that's provided more realistic outputs when you use these models.

Before I move to applications like national and project scale, I thought I'd give you a quick overview of important consideration that you need to consider when you use models. One is model initialisation. One is model parameters, and model inputs. It's very important to have this idea about what type of – what's a correct combination that you need to use for your project. If it's a national scale, the combination is different compared to like a project scale application. For example, if you look at initialisation of the model, we've been talking about carbon fractions, so you can use the measurable carbon fraction maps or, if you have the measured carbon fractions, initialise the model. And if you don't have anything, you can run the model for optimum conditions to come to (equilibrium 10:03) and use those carbon fractions (indistinct 10:05) And the same for the rate constants, you can use a default rate constant parameters, or you can use site specific ones.

And carbon inputs, so we've been talking more in the morning sessions, like what are the drivers of carbon? One is the biomass. If you're running a carbon model and if your inputs are incorrect, your modelling will be also incorrect. It's important to determine these correct inputs to the model. For example, biomass can be measured if it's a paddock scale, or it can be modelled from another model. There are issues because there is (indistinct 10:38) propagation then, and also derived from satellites.

National scale application of these models. National scale, we're using a model called FullCAM, an acronym for full carbon accounting model. The input datasets, we are using time series, climatic datasets at a one kilometre spatial resolution. Crop management and management datasets, that's including the stubble and the land management practices, mainly using ABS statistics and other census data available at a Statistical Areas 2 Level, so it's a very coarse spatial resolution. You can see that representation of wheat yield average, it's quite (indistinct 11:20) and it's just a representation for the (indistinct 11:23) and the soil data. We have (rich 11:27) digital soil map products here in Australia, so we're using those products to initialise the model, which actually reduces uncertainty significantly, so digital soil maps are practical use on carbon modelling work.

We use these input datasets, and we can put it to a model and we can run the simulations with the time. For example, FullCAM model runs with monthly times and places at a spatial resolution of 25, but we can aggregate it to like a different spatial output. If you can remember this previous slide, so in case of national scale application, we initialise the model with the measurable fractions, mapped digitally, and rate constants or the model parameters are optimised using long-term trial data. And the biomass data is actually modelled from a simple crop model based on, like rainfall. And the land management data is actually collected through census, so statistical datasets. There is quite a bit of uncertainty in terms of some inputs. But there are some good inputs at a high spatial resolution as well. But that's a national scale modelling.

If you look at the project scale, that's already specific to a carbon project, or any other project that we're thinking, it's important that national scale represents the average behaviour of the dynamics of carbon, but using those models at a direct data project scale needs to be considered at some stage. When you use these models at a project scale, we need to customise the input initialisation parameters specific to the project unless the (default 13:05) ones are working. Validation of estimation of SOC change is important using measured datasets and also quantification of uncertainties and more importantly, if you have more projects using these models, then we can use this project level data to actually improve the national scale modelling. There's the advantage of having these at project scale, these models.

I took an example from Adrian Chappell and Jeff Baldock's work on some of the site specific calibration of some of these models. Here, the example of taking the Rothamsted carbon model and example site is Brigalow in Queensland, which was cleared for cultivation in 1982. You can see there is some drop in continuous wheat cultivation after clearing, but when you have the continuous pasture, there is a drop, but there is an increase of carbon. The point that I want to make here is that here, we used two types of parameters; the four parameters, which when you run with the four parameters, it's actually reflected in a blue line; and site specific calibration, which is depicted in a black line. When you use site specific calibration and when you calculate the error accuracy of the model, that's (indistinct 14:24) we get around 0.4 tonnes of carbon, that's a half a tonne error for the continuous pasture. And for the wheat, it's like 0.29. However, this is like very site specific calibration, so we need to have temporal data to do something like that, to get some accuracy – high accuracy.

To bring your attention again to the previous slide for the model components. In terms of initialisation, here we use measurable fractions, rate constant standardised, biomass measured, and land management practices observed. Your predictions or similar results are much accurate when you use more (observed 15:05) datasets.

Quantification of uncertainty. One limitation of these models is that the uncertainty of these models are just, if you use only parameters, we get – so the red line depicts a temporal change of the carbon, only one value. But if you actually quantify the uncertainties in the (Bayesian 15:26) framework, which are things like, say example like DPM parameter, we can have an upper and lower (indistinct 15:32) of those parameters and run the model thousands of times. You get uncertainty of the parameters through the simulations. Those type of uncertainty estimation is very important if you're using these models for project level and then also for accounting purposes. And uncertainties can be used for the inference of also the risk management of the carbon (crates 15:55).

Next generation carbon models. One thing that we need to think about when you design this next generation model is actually minimise these uncertainties. We've been talking, like some of the previous talks, we'll discuss about the – we talk about the increase in carbon, but there are constraints for the production. For example, there can be no (indistinct 16:19) but there can be subsoil constraint. How do you know? We have only one value measuring. One way is getting these rich precision agriculture datasets. Most of the Australian farms, at least for the large scale production datasets, have the (indistinct 16:36) data, so we can use this (indistinct 16:38) data as a (indistinct 16:39) or the input to the carbon model. That's a possibility.

And also, there are a lot of talks about – today, like talking about mainly with the groundcover. There are satellites that measure fractional cover. For example, Sentinel-2 satellite, which measure Australia in every 10 by 10 metre area every four days, which can be used to derive fractional cover data. This example is supplied by Tom Bishop from the University of Sydney. (Southern New South 17:10) there's a farm that he has access to the (indistinct 17:12) data, which can be coupled with the carbon data, carbon models and also, the fractional cover data. You can see that temporal variation of fractional cover within a year. This is for the bare soil fraction. That type of information can be used to inform our model drivers rather than just guessing by using the remote (indistinct 17:33) datasets.

Next one is combining these datasets. Once you have this dataset, it is important to combine this. That's also a challenge, but that's important that we combine these datasets with a process-based model and also, quantify the uncertainties. Once you combine these remote (indistinct 17:53) datasets with process-based models and we have our uncertainty estimation, we can actually predict carbon with some known uncertainties. For example, this is taken from Liverpool Plains in Northern New South Wales, we have in Gunnedah catchment. This is starting level carbon and carbon fractions. And you run it for 10 years and you can calculate the change in carbon over the time, 10-year period.

With that, finally, a complete measurement and prediction system, that's actually an extension of the previous slides. We need to have (dual 18:31) reference information. It's important to actually (dual 18:34) reference all this information when you collect data. And you combine with the measurement computer remote sensing with the carbon model and then quantify it and also connect with the uncertainty (indistinct 18:46) toolbox with this carbon model and you can run your carbon model with quantified uncertainties. That's almost like a dream, but that's not a – that's the one that we need to target in our view.

That's it. And before I conclude the key take home messages, it's important to consider the model, depending on your requirement. And also, consider about model initialisation. It's very important. If you don't initialise your model correctly, you're never going to get your estimation correct. And also, the model parameters. And also, think about how you're going to quantify the uncertainties of model. Uncertainties can come from model parameters, model itself, or model inputs, so we need to consider those aspects.

Finally, I'd like to thank a few of my colleagues and the Department of Industry, Science and Energy and also the Clean Energy Regulator for some of the work that has been continuously helping us to do this work. Thank you.

Summary

This is a summary of the presentation given to the Forum on 22 April 2021, provided by Adjunct Professor Annette Cowie, NSW Department of Primary Industries.

There is increasing recognition of the potential for soil carbon management to play a key role in climate change mitigation, and simultaneously deliver additional environmental and socio-economic benefits.

Building soil carbon to mitigate climate change and meet international agreements

At the international level, the Paris Agreement (PA) targets climate stabilisation through achievement of net zero GHG emissions in the second half of the century. Soil carbon sequestration is one of the few available strategies for carbon dioxide removal, required to meet net zero and carbon neutrality targets. The Land Degradation Neutrality (LDN) initiative, one of the Sustainable Development Goals, encourages action to avoid, reduce and reverse land degradation, through sustainable land management, and identifies soil organic carbon as a key indicator of achievement of LDN.

Getting paid to increase soil carbon – integrity principles

At the national level, there is strong support for soil carbon management through the Emissions Reduction Fund (ERF), complemented by state-level initiatives. The Offsets Integrity Standards uphold the credibility of the ERF, requiring that abatement is additional and genuine. To support the criterion of conservativeness and to manage the risk of non-permanence of soil carbon sequestration, the ERF applies a 'risk of reversal' buffer, discounting for uncertainty, and further discounting if a 25 year permanence period is chosen rather than 100 years.

Emissions trading to promote soil carbon sequestration requires methods for estimation of abatement that are sufficiently accurate to ensure credibility, yet cost-effective, to facilitate participation. Development of incentives outside the carbon market will be important, to realise the full potential for soil carbon management to deliver climate change mitigation and land restoration.

Transcript

A/Prof Vanessa Wong: Next speaker is Adjunct Professor Annette Cowie. She's a Senior Principal Research Scientist in Climate Research and Development in the New South Wales Department of Primary Industries. Annette has a background in soil science and plant nutrition, with a particular interest in sustainable resource management. Annette contributes to the development of climate change policy and greenhouse gas mitigation in the agriculture sector, including greenhouse gas counting for emissions trading at state, national and international levels. She was the lead author in the IPCC special report on climate change and land, and is a lead author in the IPCC's sixth assessment report.

Since 2000, Annette has been a member of the International Energy Agency Bioenergy Research Network, and led the group Climate Change Effects of Biomass and Bioenergy Systems. She is currently coleader in the IEA Bioenergy Group, Climate and Sustainability Effects of Bioenergy within the broader bioeconomy. Today, Annette will discuss incentives for building soil carbon to mitigate the effects of climate change and meet international agreements and the integrity principles of getting paid to increase soil carbon through the ERF.

[Applause]

Adjunct Prof Annette Cowie: Thanks very much, Vanessa, and thank you to the Office of the National Soils Advocate for organising this exciting event, and for the invitation to talk to you today. After a whole day after talking about soil carbon, there isn't much that I'm going to say that you haven't heard already, but my focus will be not so much on the soil carbon science, but on the policy context that is creating drivers for increasing soil carbon.

The most obvious international driver is the UNFCCC, the United Nations Framework Convention on Climate Change, and under that, the Paris Agreement. In 2015, the world leaders got together and they agreed to tackle climate change, in particular, to try to limit global warming to well below two degrees and preferably no more than one and a half degrees. And the Paris Agreement identified that in order to achieve that, what the world needs to reach is net zero in the second half of this century. Now, you might hear people say that it's by 2050, but that's not actually what the Paris Agreement says. It's the second half of the century, and so to get to net zero, we need to balance greenhouse gas emissions with greenhouse gas removals, which in practice, means carbon sequestration.

Now, the UNFCCC asked the IPCC, the Intergovernmental Panel on Climate Change, to investigate pathways to deliver this 1.5-degree target, and this special report was released in 2018. And it looked into whether it was possible, and it said, "Well, we've already warmed the world by about one degree, but trying to limit it to no more than one and a half is definitely worthwhile, because human and natural systems will be much better able to cope if we can achieve that."

As to the question of if it's too late; well, when it came out in 2018, they basically said, "It'll take a massive, drastic reduction in our current emissions to do that, but there are a number of different pathways by which we could do it." Of course, time has moved on since 2018 and it's getting harder and harder, and you may have seen that the Academy of Science released a report that had the statement saying it's virtually impossible, which was picked up very widely internationally as Australia's decided it's not possible, and some people are questioning that. Let's hope they were wrong. But what it means is that if we're going to achieve that one-and-a-half-degree target, we're going to have to pull a lot of carbon out of the atmosphere, and that's where soil carbon comes in.

There are a range of different carbon dioxide removal strategies, and these are the seven that are investigated by the IPCC in the special report 1.5; the most obvious one that we're talking about today, soil carbon management. There's also planting trees, also very obvious. Another one is biochar, which I'd like to come back to, but the one that was most prominent in the special report 1.5 is actually BECCS, bioenergy with carbon capture and storage, and that means growing plants. They take CO2 out of the atmosphere obviously. You burn the plants, you capture the CO2 and then you do geosequestration. And for the modellers, that's a very nice way of sucking CO2 out of the atmosphere and getting it underground. There's a lot of questions now about whether BECCS was the right thing to promote and the next report won't have BECCS being quite so prominent.

Some other options that I've illustrated there are, let's say, emerging, enhanced weathering. Take basalt rock, crush it, and then spread it across the land. As it weathers, it absorbs CO2 from the atmosphere. A lot of crushing and a lot of transport, all that. DACCS, direct air capture with carbon capture and storage, so that's fans that suck air past a solvent that absorbs the CO2 and then you do geosequestration with that; lots of energy involved. And then there's the ocean options, and the one that people used to talk about was ocean fertilisation which was putting iron into the ocean to encourage algal growth with all sorts of possible implications for the environment. The one that's more prominent these days is alkalinisation, adding lime to the oceans so that you increase the pH and increase its capacity to absorb CO2. Let's call them experimental.

I said I wanted to come back to biochar. Well, it is a pet topic of mine. I wasn't expecting though that (Suze 06:01) would already have told you about biochar. I thought I might need to explain it, but let me just recap on biochar. Biochar means taking biomass and heating it in a low oxygen environment, and what you create is a substance that's pretty much like charcoal and it's very stable. It's hard for bugs to eat it, and it lasts if you use it as a soil amendment for hundreds to thousands of years.

You might think it's a bit strange to make charcoal and stick it in the soil, but the reason we're interested in doing that is because German soil scientists actually discovered that in the Amazon region, there are these terra preta soils which are very fertile and they're soils that have been anthropogenically created by the American Indians who traditionally put the remains of their fires and their broken pots and their chicken bones into the soil, and then noticed that this dramatically increased the soil fertility, and it's still fertile hundreds of years later. And so, the scientists said, "Well, if what if we made new charcoal and put in the soil? Could we get that same increase in productivity?" That's why people have been interested in the last twenty years – it's a pretty new topic – in biochar, and whether it can promote productivity. But we're interested in it today because of that stable carbon, so it is a carbon dioxide removal technology.

The illustrations there are some plants that are actually operating in Australia. You might hear that biochar is also very experimental, but there is actually a lot of biochar being made around the world, mostly in China. But in Australia, we have a plant that it is making biochar and using it in potting mix. We have the Logan Council, which is building a plant that is going to take biosolids and produce biochar plus energy, and we have a plant in Tamworth that's illustrated there as well.

Now, besides the fact that it's a CDR technology because it stabilises the carbon, biochar has been found in these experiments over the last twenty years, to have those impacts on soil productivity, that has been seen in those anthropogenic terra preta soils. It has the capacity to increase plant growth because it can increase water holding capacity, increase nutrient holding capacity. It can stabilise contaminants, both organic and inorganic, and so metanalyses that have looked at the large volume of literature that's been produced on biochar in the last twenty years have found that on average, it increases crop yields by between 10 and 40%.

But don't let me give the impression that biochar is magic. Not all biochars, in all circumstances, have that result. We're still working out where and when are the best places to use different types of biochar.

But also in relation to the climate effects, we've noticed the interesting observation that it can dramatically nitrous oxide emissions. You've heard already today how important nitrous oxide is as a very powerful greenhouse gas, and we've got results that show between 50 to 70% reduction in nitrous oxide in some circumstances.

And then, in relation to soil carbon, our topic of the day, Dan told us how microbes eat and respire CO2. (Suze) told us – in fact, we all demonstrated for her – how if you protect the carbon, it doesn't decompose because the microbes can't get to it. What we've found is that if you have biochar in the soil, with certain types of clays that are actually quite common internationally, that creates these tight aggregates that protect the organic matter, so as new organic matter is put into the soil either from decomposing residues on the surface or those root exudates, then the presence of the biochar and those clay minerals will actually attract that carbon and build the soil carbon over time, so you'll have more soil carbon than is added in the biochar itself. We call that negative priming. And as I say, the impacts do vary between biochars because biochars vary depending on what you make it from, and how you make it.

Now the next report that the IPCC produced in the current sixth assessment cycle is the Climate Change and Land report, and one of the things that we looked at there was the potential, but also the risks, in the land-based CDR technologies. What this report showed was the very close relationship between climate change and land degradation. It showed that in fact, currently, the majority of the globe is impacted by human activities and about 40% of it you could consider degraded.

We showed that soil is being lost at about a hundred times faster than it's being formed and we showed that the land degradation is largely a result of unsustainable land management in agriculture. We showed that climate change is exacerbating land degradation and for example, the increasing incidence of drought leaving land bare and susceptible to wind erosion, the increasing incidence of storms and highly erosive rainfall is leading to water erosion, and this, of course, is causing more carbon to be released as the soil carbon decomposes and limiting the capacity of the land to take more carbon out because it limits plant growth.

But on the other hand, the very close relationship between the climate change and land degradation means that if you manage land sustainability, you can increase productivity, and at that same time, take CO2 out of the atmosphere and offer climate change mitigation.

The benefits of sustainable land management to managing land degradation have been identified clearly by another of the multilateral environmental agreements, the UNCCD, the Convention to Combat Desertification, and that convention has promoted the concept of land degradation neutrality, and the idea of LDN is that at a country level, you're aiming to achieve no net loss of productive land. They promote sustainable land management as the main measure here, and they promote a hierarchy of actions to be taken at country level, where you put most effort into avoiding degradation, then reducing degradation, and finally, restoring degraded land, so that you need to anticipate how much land might be lost, as in degraded, by your current activities, and then take pre-emptive action within the same land type to restore some of that land so that you achieve that balance.

LDN is largely promoting a landscape-scale approach to managing the social ecological system, that Liz described in her talk. It's encouraging land managers and land use planning to look at the whole landscape, to encourage land to be used according to its capability, and to be establishing a mosaic of land uses across the landscape where you'd be integrating productive uses with conservation and settlements in infrastructure.

This complex figure is not intended for you to read, but it illustrates the process that we went through in trying to work out how you'd work out if land degradation neutrality has been achieved. What we mapped here was the relationship between the drivers of land degradation and the ecosystem services that we're trying to deliver by implementation land degradation neutrality. And so, the column that has the symbols in it, which is all I wanted you to see really, lists the various ecosystem services that come from the land, and the symbols represent different indicators that we could possibly use to measure LDN. And the black hexagons are soil carbon, and you'll notice a lot of them. What we identified was that soil carbon is a really good indicator of most of the ecosystem services that come from managing the land.

It was one of the three indicators that were chosen for monitoring LDN, the other being land cover change and change in land productivity, and we decided that it was important to apply these indicators in a one-out-all-out basis, so if any of these decline, then the land is considered to be degraded.

Now, the other important element, which has also been mentioned, in fact, Liz spelled it out very nicely for us; so the important element of the UN Sustainability Agenda is the SDGs of course, and Liz did indeed show us how managing soil carbon can contribute to achieving many of the SDGs.

Now, land degradation neutrality, as proposed by the UNCCD, has in fact been picked up by the SDGs. It's SDG Target 15.3. But the other one that's also important for soil carbon is Target 2.4, which is about creating sustainable and resilient food production systems – this is my abbreviation of it, it's very long – that improve land and soil quality.

Now, the countries to these conventions, that are parties are to these conventions, are obviously trying to introduce measures at national level in order to be able to achieve their international obligations. In fact, only 13 countries have explicitly identified soil carbon management under their nationally determined contributions, their actions under the Paris Agreement. But there are a lot of countries – in fact, it's 127 now – that have implemented or are discussing net zero targets, and there are, in fact, exactly the same number just coincidentally, 127 countries, that have said that they will adopt land degradation neutrality targets. And so, these countries have made these decisions and now they're looking around for how they're going to achieve it, and they're recognising the importance of soil carbon to be able to do that.

The actions are not just at government level. There's plenty of action by industry as well, largely encouraged by the fact that we have these international conventions, but there are many companies that have signed up now to programs for monitoring their greenhouse gas emissions, for demonstrating the sustainability and reductions in greenhouse gas emissions, and to take on targets.

So far, I've been talking about the international context, but of course, at the national level, we have the Emissions Reduction Fund that we've spoken about several times today. That of course is the main mechanism that Australia is taking to meet its international obligations under the Paris Agreement. You're probably all thoroughly aware that most of the project types under the ERF are in fact about reducing emissions or sequestering carbon in agricultural land.

And by far, the majority of projects to date have been about vegetation management, so this is the cumulative amount up until the last auction. I believe a year ago, there was only one project, the one Matthew spoke about earlier, in soil carbon management. But now, I believe there's 130. Does that sound right, Matthew?

Matthew: (17:50).

Adjunct Prof Annette Cowie: Yes, sorry registered projects in soil carbon. Soil carbon has become much more prominent, and one of the reasons for that is the fact of the new initiative to allow $5,000 of upfront credits to be used to cover the cost of soil carbon baseline sampling. As we've heard, it's quite expensive.

The other activity, I guess, that's being promoted by the Morrison government in order to achieve our emissions reduction targets is basically investing in technology, in low emissions technologies, and the technology investment roadmap has declared a range of priorities and soil carbon is happily one of those. And so, we have the current initiatives, the innovation challenge to reduce the cost of soil carbon measurement, and a new emissions reduction fund method being developed that will be easier, I guess. And we'll wait to see, Alex, whether it has the right degree of recognition of uncertainty.

Prof Alex Bratney: We can't be sure (18:56).

Adjunct Prof Annette Cowie: And at the state level, you're probably aware that all the states have net zero targets. New South Wales, for example, where I come from, we have a net zero 2050 target. We have an interim target of 35% reduction by 2030, and we have a range of programs which are investigating the potential for abatements, which are looking at the win-win opportunities where we can sequester carbon at the same time as enhancing agricultural productivity, and we're supporting landholders in making decisions about signing up to soil carbon trading, for example.

We also have activity by local companies. Their program, Climate Active, gives carbon neutral certification to products, to precincts, to events and to companies. There are many that have signed up to this and there's just a few of them illustrated here. We also have the National Farmers Federation; has said that they will support a 2050 net zero target, and we have the more ambitious target by the Meat and Livestock Australia of carbon neutral by 2030.

And all of those entities that are looking to become carbon neutral need to be following this hierarchy, which says that they should first reduce their emissions, secondly, they should sequester carbon within their own jurisdiction, and finally, they should offset their residual emissions by purchasing credits that can be created by projects undertaken by another entity that either reduce emissions or increase removals.

And Beverly has already introduced this, so I really don't need to say much, but any scheme that is offering carbon credits needs to maintain credibility, and they all have a list of criteria to demonstrate integrity, and Beverly went through the list, so I don't need to go there, and I noticed Vanessa's probably giving me a hurry up there.

I will just mention that these are obviously necessary in order to have confidence by those who are purchasing the carbon credits, and to give credibility to the scheme. As Beverly said, it does have a lot of credibility internationally, but they also create a big challenge for soil carbon, also been mentioned. The first one is the permanence. We've heard from everybody that soil carbon is actually vulnerable. You can increase soil carbon, but if you do, because you can't see it, you can't know whether you've lost it or not. We do have a permanence requirement of a hundred years, or another alternative, you can choose 25, but you get a discount of 20% for doing that. We have a risk of reversal buffer of 5% maintained to allow for that possibility that soil carbon is lost. We have a very rigorous approach with detailed requirements on how to do that soil sampling and how to measure the samples. We have the discounting for uncertainty that Beverly describing. In fact, applying exactly what Alex told us we should be doing. And we do deduct any project emissions for those non-CO2 emissions that we heard about.

But because we go through that whole exercise, it can be a bit off-putting and it's certainly expensive. Hopefully, the new initiatives to reduce the cost of soil sampling, or soil carbon measurement, and to introduce the new method under the ERF, will make it more attractive. But I would suggest that there will still be landholders who won't be convinced that they want to sign contracts to enter into emissions trading. There will be some that want to keep the carbon to make their own carbon neutrality claims, and there will be some who are just too small for it to be a viable prospect. What we're going to need is other incentives to overcome barriers to adoption of these practices, so that we can capture the full range of landholders out there in order to encourage them to increase soil carbon, to deliver the benefits that we've heard about from everybody today.

We'll just conclude then by saying that there is a convergence, firstly of the pressures: climate change, land degradation, loss of biodiversity, increasing population, concerns about food security. There's a convergence also of the initiatives and the responses to this under the Paris Agreement, Land Degradation Neutrality Initiative, the SDGs, carbon neutrality claims, net zero targets, the ERF, and these are all identifying the pivotal role of soil carbon in contributing both to enhancing land productivity and sequestering carbon contributing to climate change mitigation and also to climate change adaptation. But in order to actually capture this and to deliver that on that potential, we need – as everyone has already said – we need cost effective methods for monitoring and verifying soil carbon change, we need our land managers to have the knowledge and capacity to undertake the practices that increase soil carbon and to manage the risk associated with getting involved in emissions trading. And we need policy incentives that are going to overcome those barriers to adoption and I'm suggesting that these incentives can be within emissions trading, but also go beyond it in order to be able to capture the full potential of the benefits from increasing soil carbon that we know are undoubtedly out there. Thank you.

[Applause]

Transcript

A/Prof Vanessa Wong: I've been given the job of summarising the last sessions or last couple of sessions of talks. And I know that we've given you a lot of information, a lot of very dense information and in some cases, we've given you enough information which normally takes an entire PhD to get your head around, and we've given all of that to you in a day. Hopefully there are some key messages that you'll be able to take from this and I'll pull out some of those from these last couple of sessions.

What I was asked to do was to summarise those talks and really look at answering the question, what realistically can we achieve knowing what we know now and with the techniques that we have now?

But to start off with, why is it so complicated? Because at some point in time, somebody probably thought, well maybe we could just go out, get a number and apply it to a model and then we're all happy and off we go. And it's really complicated because Australian soils vary across the landscape, both in terms of space and in time. And that's a common theme that has sort of run through all of these talks. And soils vary across space, particularly because of these gradients that we see in terms of climate. So we have rainfall gradients, in terms of where we move from the internal part of – or the interior of Australia out to the coast, and then these north/south gradients and we also have temperature gradients as well. So again, looking at this continentality.

The underlying geology varies across Australia, and that underlying geology is what soils form on. So we have this diverse range in soils which means that the soil carbon processes or the distribution of carbon also varies because those soils really drive net primary productivity and it drives vegetation growth which then influences soil organic inputs and those microbes that consume organic matter. It means that the distribution is different and also the processes are different as well, in terms of the rates of change. But we know that there are these general patterns. Like I said, we have these gradients. We know that rainfall is highest up in the tropical north and it decreases as we move into the interior of Australia. So we can estimate those types of processes of what actually happens as we move from different regions around Australia.

We are also measuring a really small change in soil organic carbon against a reasonably large background value which was mentioned. Just, I guess to put that into context, it's kind of like if I grabbed a can of coke, which I learnt this morning has 16 teaspoons of sugar in it, gave it to you – well actually added half a teaspoon of sugar, gave it to you and asked you to tell me how much sweeter it is or determine the change in sweetness, trying to determine that – looking at the effect of that half teaspoon against that background of 16 teaspoons. So, we are trying to look at that very, very small change against quite a large background.

We also want to have confidence in terms of the sampling and what we've seen is that we have reasonably robust methods in terms of the measurements once we get into the laboratory and we have very good consistency with the laboratory analysis. But getting a representative sample and knowing when to get that representative sample and how that representative sample reflects your landscape or that point in time, is really a big challenge. So, sampling really needs to be reliable. It needs to be standardised and it needs to be repeatable as well. We need to be able to know that what we have represents that landscape.

And we know that there are loads of different methods to measure soil organic carbon and how do you know which one to choose? There's laboratory methods, there's field methods, there's proximal sensing, there's remote sensing and then there's 250 models that we can also select from, so which one do we actually choose and how do we choose any of those methods? And I'll get back to that.

Seeing below the surface is also really challenging as well because what we see at the surface doesn't necessarily reflect what's happening below ground. And we've heard from a couple of different talks about constraints or subsoil constraints. So, whether there's a subsoil acidity constraint or subsoil compaction, those constraints below the surface, we can't actually see. So, what we're looking at is this build up of carbon at the land surface. We're measuring the soil organic carbon, but we really don't know what's happening below the surface until we start to look at – until we start to sample, and again it comes back to that sampling challenge. And because we have these subsoil constraints and the way that soils vary across the landscape, the amount of soil organic carbon stock, really depends on what also happens at depth as well. Because when we measure soil organic carbon stock, we tend to measure it, as was alluded to earlier, to a depth of about 30 centimetres and usually soil scientists are looking at measuring soil carbon to a depth of at least a metre.

But the stock that you have depends on not just the carbon content, so the concentration that you're measuring or the number that you get as you put it through the analytical machine in the lab, but it also depends on the water content, the depth of sampling, because the deeper you sample and the deeper that you report, the more carbon you have. And also the bulk density which again, we've all alluded to, and I'm not sure that anybody actually really explained what bulk density was. So bulk density is the amount of soil, a known weight of soil in a known volume. If you put, for example, in your glass, if you put soil or you put some sand in that glass and you weigh it, say you have 200 grams of sand in that glass, then you have – and measure the carbon in that glass which might be 5% and then convert it – then you convert the weight of sand relative to that volume of the glass, then you have a standardised value. If you squash that sand and try and force more sand into the glass then you're going to have more soil and that increases the stocks. The more soil you have or the more squashed soil you have, the more you have – the more carbon you could potentially have depending on that content, the carbon content. So, the bulk density is really important. And this varies across the landscape and it also varies with depth. And again, this goes back to the sampling strategies that need to be reliable, standardised and repeatable.

How do we know if the change is real? So again, we've seen lots of different figures that show a lot of variability in carbon whether it's organic carbon content or organic carbon stocks. How do we know that that change is a real change? And Brian covered a lot or summarised a lot of those studies, generally those changes in management practices in terms of altering the amendments or changing the rotation in those fields generally had a small or modest impact on soil organic carbon. But the key point that came out of that was that soils under perennial pastures or continuous cover in that vegetation at the land surface, generally had higher soil carbon levels than those of annual crops which are removed year by year. And changing that land use would generally have a greater impact on soil organic carbon than changing those management practices. So, shifting, again, from cropping to pasture will have a much greater impact than changing the type of amendment or shifting from what we would consider or what we normally call conventional practices to organic practices.

But, again, this has sort of been really common throughout today, the magnitude of that increase is really tightly constrained by geographical factors. So, the climate of a particular region and the soil type and importantly the clay content of your soil, will really restrict the magnitude of that increase and what you can actually do in terms of building carbon and potentially the limit in terms of the amount of carbon that can be stored.

And again, we don't really know how we can keep it there for longer timeframes. This issue of permanence will continue to come up for some time. There is no single silver bullet. Reliable measurement soil carbon requires a good understanding of a landscape and we need that good understanding of our landscape to ensure that we sample properly so that we can have these reliable measurements of carbon, so that we can continue to monitor and monitor that change over time.

There is no single amendment. There is not single land use change. And there's no single land management practice that will result in a universal increase in soil organic carbon. It really is horses for courses. The regions in which you are working in have particular characteristics in terms of climate and soil type, and those are the constraints that we need to work in.

How you measure soil organic carbon, as I said, there are lots of different methods. There are lots of different models. How you measure soil organic carbon really depends on what question you want answered or what question you were asking, and other considerations, like how large is the area you want to measure? What sort of precision do you need or what sort of precision do you want and how accurate does that measurement need to be? Because we can measure carbon to multiple decimal points with a certain level of uncertainty, but do you really need that? So again, it comes back to what question are you asking, but the methods that we have, depending on that level of precision and the accuracy that you're after, they're robust, they're repeatable, they're verifiable provided that they're applied and executed appropriately. And there's a number of people in this room who can assist with that.

And finally, there are benefits well beyond carbon sequestration, which again has been alluded to in a number of talks. We have a great potential and a great opportunity to restore degraded lands. So, if we go back to that glass example that Dan talked about earlier, where you have a finite capacity to store carbon in your glass. So, your glass has a finite capacity to hold a certain amount of water, those degraded lands probably don't have a lot of water in them. So, we have the potential to fill those glasses with more water because they are degraded. So, there is a real opportunity there to restore those degraded lands.

We know from what Sue was saying that maintaining vegetation cover will build organic matter, and it will also enhance a whole lot of other property as well. So, it will improve soil fertility and it will improve soil structure which will protect that carbon. And increasing soil organic carbon will ultimately improve both our aboveground environments in terms of biodiversity benefits and also our belowground environments as well. There's demonstrated benefits in terms of improved resilience to disturbance and improved resilience to natural hazards like flood effects, drought effects and also fire as well in both agricultural landscapes and in those natural environments. We've focused a lot on agriculture and those natural environments tend to get forgotten in a lot of these talks. So improving resilience is also really important.

We know that productivity in those production systems is enhanced by improving organic carbon and organic matter because it does improve soil fertility and that ecosystem function is sustained. So there are, I guess, much broader environmental benefits and agricultural benefits and productivity benefits in terms of looking at building organic matter to increase organic carbon beyond just this carbon sequestration question.

I will leave that there, and I'd like to invite Penny up to the stage to facilitate our final discussion panel.

Soil Organic Carbon: Realities and science for policy advisers and decision-makers

Program

Welcome and opening addressThe Hon. Penny Wensley AC, National Soils Advocate

Transcript

Part 1a: The science behind SOCDr Liz Clarke, CEO, Soils for Life

Transcript

Part 1b: The science behind SOCAssociate Professor Frances Hoyle, University of Western Australia

Summary: Parts 1B and 1C: The science behind SOC

What is SOC?

What is its function in the soil, linkages to soil health?

Impacts on SOC content

What is the probability of successfully increasing SOC?

Transcript

Part 1c: The science behind SOCProfessor Dan Murphy, University of Western Australia

Summary: Parts 1B and 1C: The science behind SOC

What is SOC?

What is its function in the soil, linkages to soil health?

Impacts on SOC content

What is the probability of successfully increasing SOC?

Transcript

Part 2a: Consideration of the complexitiesDr Sue Orgill, NSW Department of Primary Industries (Featuring David Marsh)

Summary

Permanence in soil

Vulnerability to Loss

Impact of climate change on soil carbon stocks and flows

Transcript

Part 2b: Consideration of the complexitiesProfessor Peter Grace, Qld University of Technology, delivered with Associate Professor David Rowlings, Qld University of Technology

Summary

Considerations of GHG emissions when increasing soil organic carbon (SOC)

Previous Government research on agricultural GHG emissions and SOC

Effects of increasing SOC on nitrous oxide (N2O) and methane (CH4) emissions

Transcript

Summary of Parts 1 and 2: The complexities and considerations of adoptionDr Michael Crawford, CEO, Cooperative Research Centre for High Performance Soils

Transcript

Part 3a: Setting expectations, measuring, estimating and modelling SOCAdjunct Professor Beverley Henry, Qld University of Technology

Summary

Why quantify SOC?

Why is it so complex?

Why is quantifying SOC so expensive?

Can the cost of quantifying SOC be reduced in the future?

Transcript

Part 3b: Setting expectations, measuring, estimating and modelling SOCAssociate Professor Brian Wilson, University of New England

Summary

What research can we draw from to quantify changes in Soil Carbon?

What is the impact of management change on SOC?

What is the impact of changes in land use on SOC?

What does this mean?

Transcript

Part 3c: Setting expectations, measuring, estimating and modelling SOCDr Mark Farrell, CSIRO

Transcript

Part 3d: Setting expectations, measuring, estimating and modelling SOCProfessor Alexander McBratney, Sydney Institute of Agriculture

Summary

Estimating SOC at the paddock scale

Differences in SOC estimation methods

Confidence levels of estimating SOC

Transcript

Part 4a: Changing SOCDr Senani Karunaratne, CSIRO

Summary

Why do we need soil organic carbon models?

National vs. project scale modelling

Next-generation soil carbon models

Transcript

Part 4b: Changing SOCAdjunct Professor Annette Cowie, NSW Department of Primary Industries

Summary

Transcript

Summary of Parts 3 and 4: What can realistically be achieved?Associate Professor Vanessa Wong, President, Soil Science Australia

Transcript

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