Case study - Demystifying nitrous oxide (North)

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

Nitrous Oxide Research Program (NORP)

Demystifying nitrous oxide

Results from a national research program not only quantified Australia’s nitrous oxide (N2O) gas emissions, but also helped farmers develop new ways to manage the gas.

Professor Peter Grace from Queensland University of Technology who headed the Australian Government’s Australia’s Farming Future Nitrous Oxide Research Program (NORP), said N2O is emitted naturally from the microbial processes in the soil, however, the majority of N2O emissions come from human activities, with much of this resulting from agriculture.

While traditional greenhouse gas emissions research focused on carbon dioxide, Professor Grace said data on N2O soil emissions from Australian soils is limited. “Nitrous oxide is effectively 300 times more potent than CO2 when it comes to global warming. That is why the NORP is so important,” Professor Grace said.

“The NORP brought together researchers who measured and modelled N2O emissions for dryland and irrigated farming (particularly grains, cotton, sugarcane and dairy) from sites right across the country.  N2O is a good indicator of overall nitrogen use efficiency, so the research outcomes are a win-win in terms of reducing emissions and increasing profitability.

“From that we then developed a range of tools and specific management techniques for each individual land-use type and climatic condition that farmers, consulting agronomists, extension officers and policy makers can use to manage, and hopefully reduce, these potent emissions as well as improving nitrogen use efficiency.”

Funded through the Australian Government’s Department of Agriculture, Fisheries and Forestry under the Climate Change Research Program, the NORP partners included the Department of Primary Industries Victoria, the Grains Research and Development Corporation, Dairy Australia, Department of Primary Industries New South Wales, the Queensland University of Technology, the Queensland Department of Environment and Resource Management, University of Melbourne and the University of Western Australia.

Professor Grace said N2O research conducted at six core field sites including Mackay and Kingsthorpe in Queensland, Tamworth in New South Wales, Hamilton and Terang in Victoria and at Wongan Hills in Western Australia. He said this is important as N2O emissions greatly vary depending on the environment and industry, ranging from from less than 0.03 kg N/ha/day in the coarse textured dryland cropping soils of the Western Australian wheat belt to up to 1 kg N/ha/day from fertile soils of south-eastern Victoria under dairy production.

N2O emissions from Australian sugarcane soils are also considerably higher than other cropping systems. Professor Grace said this is potentially due to the amount of trash retained in the system and the fact that N2O losses are higher when there is a lot of water in the system.

“The results in northern trials indicate that N2O emissions seem to spike directly after irrigation. When you apply water, whether it is in the form of irrigation or just a higher rainfall zone, there is a greater potential for water logging,” Professor Grace said.

“When certain microbes are starved of oxygen, they look for alternative forms of energy, which leads to a faster rate of breakdown and an increased potential for gaseous losses of nitrogen. More water also means larger crops and potentially more biomass, which is a great source of carbon which drives the whole process, regardless of industry.”

Professor Grace said trials conducted in Kingsthorpe on the Darling Downs have compared N2O emissions in wheat and cotton crops under dryland and irrigated conditions. He said N2O emissions in wheat trials ranged from 0.23 per cent (of the total nitrogen fertiliser applied) under dryland conditions to 0.38 per cent under full irrigation. A similar range in emissions was found in the cotton trials.

Irrigated cotton farming systems have previously been labelled high-risk agricultural systems with respect to gaseous losses of nitrogen, due to their heavy reliance on nitrogenous fertilisers and irrigation to maintain production levels.

“Our field data suggests that cotton and dryland cereal production systems are actually low emitters of N2O, because those cropping systems do not return large amounts of residue and the soil carbon stocks have declined,” Professor Grace said.“While these are relatively small numbers in terms of N2O, they indicate there could be potentially larger emissions of nitrogen compounds, which are not greenhouse gases but still have a major impact on nitrogen use efficiency and profitability.”

With the development of the Carbon Farming Initiative, farmers are trying to retain more carbon in their soils, which then means there is an increased potential for N2O emissions. However, Professor Grace maintains there are a range of management techniques that cotton farmers and other farmers more generally, can adopt to reduce N2O emissions from agricultural soils.

“For example, splitting applications of nitrogen fertiliser and increasing irrigation water use efficiency is increasing across the cotton industry and its positive impact on reducing emissions is obvious,” he said. “Changing the type and amount of nitrogenous fertiliser that they apply to their soil may also help reduce potential losses.”

Professor Grace said chemicals such as Dicyandiamide (DCD) were being used in dairy systems to inhibit N2O production and the results were promising. Trials in the high rainfall zone of Victoria indicate applying DCD to the pastures surface can result in reductions of nitrous oxide of between 35 and 45 per cent and trials of Entec (DMPP) slow-release nitrogen fertilisers in crops in the northern grain region have cut N2O losses from fertiliser by up to 90 per cent.

He added planting legumes, reducing nitrogen fertiliser inputs to match crop demand and improving irrigation practices are also practical strategies farmers can implement to reduce N2O losses.

“Australia has a great diversity of soils, a variable climate and vastly different management strategies between regions. That’s why the research is vital if we are to develop evidenced-based mitigation strategies to reduce N2O and at the same time increase nitrogen use efficiency and profitability,”  Professor Grace said.

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

“A lot of farmers in this district are getting into mixed farming systems and take advantage of the seasons when they are more favourable for cropping or grazing,” Dr Bell said.

“Our research investigated how farmers manage the legume residues, how they calculate the amount of fertiliser needed to top up the legume residues and how they manage the nitrogen fertiliser to minimise potential nitrous oxide losses.”

Dr Bell said when farmers come out of grazing and back into cropping they aren’t 100 per cent 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. This means there was a legume every second year so growers didn’t have to apply a lot of nitrogen fertiliser, because it was coming out of the legume crop,” he 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 are different. So they tend to err on the side of caution and apply more nitrogen than they really need.

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

Dr Bell said they evaluated which mix of legumes and grass minimise nitrogen losses.

He said the results indicate that when legumes are included in the pastures, there is more nitrogen available to breakdown so farmers don’t need to apply as much fertiliser.

Although that’s a cost saving to farmers, Dr Bell added that physically applying nitrogen means farmers can do it when the crop actually requires it.

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

“The trouble is that this is farming and you really have no control over the rate at which legumes break down and release nitrogen.

“So if it rains after you’ve killed your pasture, but before you’ve planted your crop, then the legume residues begin to mineralise nitrogen before there is anything to take it up, meaning the risk of loss can be quite high.”

“Conversely when you apply nitrogen fertiliser, you may be adding a larger amount in one operation, but at least you should be doing it when the crop is more likely to utilise it,” Dr Bell said.

He said the mixed grass/legume pasture is perhaps showing the most promise in terms of 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,” Dr Bell said.

“So it is less risky in terms of gaseous lose​s. But the farmer still has to apply fertiliser, because the pasture residues won’t meet the entire demand of the crop.”

Dr Bell said while some early work to quantify the total amount of nitrogen being lost from farming and grazing systems has been done, more comprehensive sampling is needed.

“Under the Federal government’s National Adaptation and Mitigation Initiative (NAMI), we’ve done 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,” Dr Bell said. 

Last reviewed: 4 November 2019
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