Case study - On-farm research gets to the bottom of soil health

​Case study – Department of Agriculture, Fisheries and Forestry, Australia’s Farming Future Climate Change Research Program (CCRP)

National Adaptation and Mitigation Initiative (NAMI)

On-farm research gets to the bottom of soil health

Research conducted at farms across the country has helped equip farmers to adapt and adjust to a changing climate.

The Department of Agriculture, Fisheries and Forestry commissioned the Grains Research and Development Corporation (GRDC) to manage the National Adaptation and Mitigation Initiative (NAMI) — a $9.5 million project designed to take the research out of the lab and into the paddock.

Dr David Lawrence, Principal Extension Officer with the Queensland Department of Employment, Economic Development and Innovation (DEEDI), said the NAMI helped farmers understand climate change and provided them with practical ways they can adapt to long term climate change and seasonal variability.

“NAMI projects were carried out right across Australia, but in Queensland we focused on managing Nitrous Oxide (N2O) emissions and increasing soil carbon levels,” Dr Lawrence said.

N2O gas is emitted naturally from the microbial processes in the soil. However, the use of nitrogenous fertilisers and the return of animal dung and urine in agricultural activities increase the soil content in mineral nitrogen which in turn increases the rate at which bacteria release N2O.

“Applying nitrogen is a significant cost for many farmers in Queensland. But if it breaks down and escapes as gas, it means that much of their hard earned money is ending up in the atmosphere,” Dr Lawrence said.

Nitrous oxide losses are not good because it is about 300 times more potent than carbon dioxide (CO2) for warming the atmosphere. However, N2O is also an indicator of much bigger N2 losses which is of direct economic concern to farmers.

Dr Lawrence said part of their research looked at the role that forage legumes and grasses can have in a modern farming system.

“We were able to show that using legumes during a ley pasture phase can actually reduce daily nitrous oxide emissions,” he said.

“When the plant material decays it releases nitrogen slowly into the soil, which the following crops will then use to grow.”

“It means that farmers are less likely to have a really big pool of available nitrogen in the soil at once which, given the right seasonal conditions, could be lost as a gas.

“In a future carbon economy where energy-rich products such as fertiliser are likely to become more expensive, forage crops and legumes may become an attractive alternative, because they will be cheaper and contribute less to greenhouse gasses.”

Dr Lawrence said the research was conducted at three sites in Queensland including Roma in the west, at Chinchilla on the Darling Downs where rainfall is usually higher, and at Kingaroy where the soils are better draining.

“These three locations gave us a good cross section of soil types and conditions in Queensland’s grain belt. And it meant that farmers were more likely to believe the results than if they were just in one location,” he said.

Dr Mike Bell, Principal Research Scientist with the Queensland Alliance for Agriculture and Food Innovation (QAAFI) at the University of Queensland, worked with farmers around the Kingaroy district to develop management strategies to minimise nitrogen fertiliser losses from crops and pastures.

“A lot of farmers in this district have moved into mixed farming systems in response to increasing rainfall variability. However, they still want to retain enough flexibility to be able to take advantage of the seasons when they are more favourable for cropping or grazing. This means developing management systems that will allow quick shifts between cropping and pasture phases,” Dr Bell said.

“The atmospheric nitrogen fixed by forage and pasture legumes plays an important role in maintaining the productivity and profitability of the grazing phase, but also in the fertiliser requirement of subsequent cropping operations,” he said.

“Our research investigated how farmers can manage the legume residues and any additional nitrogen fertiliser to optimise crop productivity and profit, but also to minimise potential losses to the environment.

“Nitrous oxide losses are a key loss pathway in this situation, and devising ways to calculate the amount of fertiliser needed to top up the legume residues without increasing potential nitrous oxide losses was a key focus of our work.”

Dr Bell said currently, when farmers come out of grazing and back into cropping they are not completely sure how much nitrogen they really need to apply.

“Most growers in the Kingaroy district used to grow peanuts and then corn or sorghum in rotation. There was a legume every second year to top up soil nitrogen reserves, so growers didn’t have to apply a lot of nitrogen fertiliser because it was coming out of the legume residues,” Dr Bell said.

“But now that people are moving into more forage sorghums or grass pastures with only a small amount of legume in it, their calibrations need to be different. There is a tendency to err on the side of caution and put more nitrogen on than they really need,” he said.

“I guess what we tried to do is highlight the risks of doing that but at the same time designed tillage and application strategies that would minimise that risk.”

Dr Bell said so far they have evaluated which mix of legumes and grasses maximises nitrogen returns, and have started to explore how to manage subsequent fertiliser use to minimise nitrogen losses.

He said the results indicate that when legumes are included in the pastures, there is more nitrogen available to break down, so farmers may not need to apply as much fertiliser.

Although that is a potential cost saving to farmers, Dr Bell added that physically applying nitrogen fertiliser means farmers can be sure the nitrogen is available when the crop actually requires it.

“In an ideal environment, plant-available nitrogen would be trickled into the soil at the same rate as the crop requires it. This means the system would be in perfect balance and the chance of nitrogen escaping negligible,” Dr Bell said.

“The trouble is that in rainfed farming systems you really have no control over the rate at which legumes break down and release plant-available nitrogen.

“So if it rains after you have killed your pasture but before you have planted your crop then the legume residues begin to mineralise nitrogen before there is anything to take it up, meaning the risk of loss is quite high. Conversely, if conditions are dry up until planting there may be very little nitrogen mineralised from the legume residues.

“This is a different situation to applying nitrogen fertiliser in this district, which is typically done on two occasions — at planting and then a side dressing application with inter-row cultivation about a month later. This second application can be a large amount, but at least it is done when the crop is more likely to utilise it.”

He said the mixed grass/legume pastures have the most potential for slowing down the release of nitrogen.

“The grass actually slows the release rate of nitrogen because the microbes compete a bit more effectively, so you end up with a trickle feed rather than a big flush of nitrogen like you do when you have a pure legume sward.

“On the face of it, it should be less risky in terms of gaseous loses. However, due to the slower release rates the farmer may have to apply nitrogen fertiliser to meet the peak demands of the crop, and so the risks go up again. Understanding and managing these dynamics is the key to the current research.”

It was back in 1996, that cattle producer Donald Bell first planted a mixed sward of legumes and grasses on his 2053 acre property 'Lallalindi', near Chinchilla.

“When we first moved here in 1991 the property was heavily cropped and grazed,” he said.

“We tried to do a bit of cropping, but it was so dry that it was just a waste of time and money.”

He decided to plant a mix of bambatsi grass Panicum coloratum, desmanthus Desmanthus virgatus and Lucerne Medicago sativa.

Mr Bell said although they don’t have any baseline data he is confident the mixed grass/legume pastures have had a positive effect on nitrogen levels.

“The nitrogen levels would be fairly low back in 1996 because a lot of the paddocks had been cropped for such a long time,” he said.

“The soil structure was pretty ordinary. One paddock in particular was eroding so badly that it would just turn to dust.

“Although I still don’t think the nitrogen levels are fantastic, they are a little bit better than the district average. But it doesn’t happen overnight, it can take a long time to rebuild nitrogen levels just through pastures.”

Mr Bell said his cattle are performing well on the mixed grass/legume pastures.

“We regularly achieve 1 – 1.5 kilograms per day liveweight gain. To get anything over 1 kilogram per day per beast on grass in this environment is wonderful.”

He said the initial expense of planting the pasture was quite high. Adding the desmanthus seed was so expensive back then that he only planted it out at a rate of 70g per hectare.

“Although the initial expense of planting a pasture seems fairly high, if you take into account the fact that I haven’t spent a dollar on that paddock in terms of fertiliser over the past 15 years, then it ends up being really, really cheap and we are getting great results from the cattle we graze on the paddocks.”

Mr Bell said he has also found that mixed grass/legume pastures are fairly resilient.

“Two years ago we were virtually destocked. We had about 30 cattle and four million kangaroos on the place,” he said.

“At that point I thought I had lost the pastures but when the seasons turned around they regenerated, which was fantastic news.”

While they have done some early work on quantifying the total amount of nitrogen lost from farming and grazing systems, more comprehensive sampling needs to be done, according to Dr Mike Bell.

“Under the NAMI, we did some manual measurements, but it only gave you a snapshot of the nitrogen losses on a particular day,” he said.

“Under the Nitrous Oxide Research Project (NORP) we used automated measuring chambers so as to quantify the losses in terms of kilograms per hectare over the entire growing season.”

In addition to the role of legumes in controlling nitrogen losses, David Lawrence, said the NAMI project evaluated the use of inhibitors and slow-release nitrogen fertilisers such as Entec and Green Urea.

The research was carried out at six locations including Tamworth, Spring Ridge, Bithramere, Pine Ridge and Emerald Hill in New South Wales and at Colonsay in Queensland.

“We were able to show that using these slow-release nitrogen fertilisers can cut nitrous oxide losses from fertiliser by 90 per cent,” Dr Lawrence said.

“With carbon pricing and increasing energy costs, these inhibitors may have real potential for farmers down the track to reduce nitrous oxide and overall nitrogen losses.”

In addition to the emissions work, Dr Lawrence said the NAMI project in Queensland also helped farmers to develop strategies and identify practice changes that may increase soil carbon stores.

“Traditionally, farmers in this neck of the woods crop the country until they need to apply fertiliser and then they put it back to pasture,” Dr Lawrence said.

“But what we’ve found is that when people do that they often don’t have enough nutrients, especially phosphorus, to grow decent legumes. Unfortunately, their pastures can remain pretty ordinary with low productivity and little benefit to soil organic matter and soil carbon until they fix it. So mixed farmers really need to maintain their soil nutrients to ensure they have the flexible and productive options in the future.”

Dr Lawrence said in the past there has been concern about over-cropping land and burning paddocks out but he maintains that for soil carbon the science is actually indicating the opposite may be true.

“If you are trying to boost soil organic matter, the amount of dry matter you produce and put back into the soil actually determines the levels of soil organic carbon.

“So growing more crops, and returning the stubble, roots and dry matter back into the ground may actually increase soil organic matter.”

He said rather than burning paddocks or removing stubble for hay or green chop, producers should be trying to keep as much ground cover on their paddocks as possible.

“If there is no other way of getting through the stubble then the occasional stubble burn won’t cause you too much grief,” he said.

“But if you want to run your soil organic matter down, burning your paddocks every year or making hay every year and then having a really long fallows with no cover on it, would be the quickest way to do it.”

The NAMI project has nearly 70 documented strategies of how farmers in Queensland plan to manage any possible climate change.

“It ranges from using better pasture and crop agronomy to simply ignoring it,” Dr Lawrence said.

“But however they plan to cope with future climates, the NAMI project helped them gain the necessary skills to increase the sustainability of their farms and manage a variable climate in the long term.”

Last reviewed: 4 November 2019
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