NEW research is showing the way for farmers to cut both their nitrogen fertiliser bills and greenhouse gas emissions from their farm.
The research into nitrous oxide emissions on grain growing properties hopes to show that more efficient use of nitrogen on-farm not only saves the business money, but also limits the amount of greenhouse gas released from the soil during the growing season.
The Grains Research and Development Corporation (GRDC) is supporting a number of nitrous oxide research projects, including two in Victoria involving the Victorian Department of Primary Industries (DPIV), and the Federal Department of Agriculture Fisheries and Forestry (DAFF).
DPIV research scientists Patricia Hill and Sally Officer are working on projects measuring the rate of release of nitrous oxide from cropping systems in different environments and under different crop management regimes.
Dr Hill said the research would deliver important information to grain growers, not least of which was how to make better use of the available nitrogen before it is released to the atmosphere as nitrous oxide, a greenhouse gas 300 times more potent than carbon dioxide.
“Any nitrous oxide that’s lost from the soil represents an economic cost to the farmer, because losing nitrogen from the soil is a loss of fertiliser that was once applied,” she said.
“There’s two ways of looking at it: it’s an efficiency gain for the farmer in reducing nitrous oxide emissions, but it also about reducing the environmental impact.”
Dr Hill’s research in the Horsham district of Victoria’s Wimmera forms part of the National Adaptation and Mitigation Initiative (NAMI), which involves the GRDC, DPIV, DAFF, the Department of Agriculture and Food Western Australia (DAFWA), the Birchip Cropping Group (BCG), and Queensland’s Department of Employment, Economic Development and Innovation (DEEDI).
The research is focusing on the medium rainfall zone of Victoria – an area from Warracknabeal through to the southern Wimmera which receives 375-450mm of rain a year – and the influence of farm practices on nitrous oxide emissions, including the use of tillage, spreading urea fertiliser, and the role of crop rotations in fixing nitrogen in the soil.
“The project is trying to understand what sorts of things farmers can do to reduce their emissions or adapt to an environment of increased seasonal variability. We’re trying to find out which sorts of systems are associated with the least emitting situations,” Dr Hill said.
“For example, if your management system uses a mechanical fallow involving tillage, there’s a possibility you’re losing more nitrogen than if you’re using a chemical fallow instead.”
Trials have been held on the property of Horsham East grower group member, Keith Fischer, who became involved to learn how to reduce his inputs costs at his property “Oakbank”, and to gain a better understanding of how crop rotation influences productivity and greenhouse gas emissions.
“I decided to get involved in the field trials to get information about what emissions I’m losing out of our soils, in particular the nitrogen I’m putting in, and how much am I losing to the atmosphere,” Mr Fischer said.
A corresponding trial is being conducted in high rainfall zone (HRZ), involving the Hamilton Branch of the Southern Farming Systems Farmer Group.
During the field trials, nitrous oxide release is captured using PVC pipes, which stand vertically in the ground for two days prior to the gas sampling periods. The pipes are then capped to trap the gas, with samples taken four times over the course of an hour for each chamber.
“We collect data monthly and after major rainfall events,” Dr Hill said. “The rainfall event data is to estimate the maximum emission we might ever expect, and the monthly data is to make sure we measure the seasonal variations and when the nitrous oxide comes out of the soils through the year.”
High rainfall events, which saturate the soil and prevent microbes from accessing oxygen, can trigger nitrous oxide release as the soil enters a state of de-nitrification, according to Dr Sally Officer, from DPIV at Hamilton.
“The main drivers of nitrous oxide release are the temperature in the soil, the amount of water, the amount of soluble carbon and the amount of nitrogen,” Dr Officer said.
“It’s a moving combination and basically it’s about whether the microbes have the conditions that they need. The microbes that produce the most nitrous oxide don’t like a lot of oxygen mixed in the soil so, when it’s wet and they have plenty of nitrogen, they can start really blasting out the nitrous oxide.”
The influence of rainfall events is a key feature of Dr Officer’s research at Hamilton in the HRZ, where 680mm of rain falls each year on average, mainly during winter.
An increasing proportion of land around Hamilton is being planted to crops, but the process of changing land use from pasture to cropping carries major ramifications for greenhouse emissions.
“Under climate change this area is supposed to get a little bit drier, but as conditions up north are forecast to become worse, there may be a shift to more cropping in the southern high rainfall zone,” Dr Officer said.
However, due to the natural high rainfall and the fact that many grazing areas have previously been planted with clover and grass pasture, there are already high levels of nitrogen in the soils derived from legume fixation.
“We wanted to capture that transition from legume rich pasture to cropping cereals and measure the associated release of nitrous oxide,” Dr Officer said.
“It seems that our process of spraying out the grass and encouraging the clover before we crop has really bumped up the available nitrogen. This creates excellent conditions for growing wheat, but also great conditions for creating nitrous oxide.”
Nitrous oxide emissions in excess of 3kg/hectare/year (equivalent to 930kg of carbon dioxide equivalents) were previously measured when a high fertility legume pasture in this zone was sprayed out and cropped with wheat.
This compares to less than 0.45kg of nitrous oxide/ha/yr measured in the drier cropping regions of Victoria.
The current project is looking at methods of reducing these relatively large emissions from the HRZ.
Dr Officer is measuring the impact of disturbing the soil on greenhouse gas release by planting the crops using either direct drilling or after conventional cultivation. The project is also measuring the impact of a nitrification inhibitor, dicyandiamide (DCD), which temporarily shuts down the microbes in the soil that convert ammonium to nitrate, and thus slows the rate of nitrous oxide emission from the soil.
“DCD very specifically sends the nitrification bugs to sleep,” Dr Officer said. “The microbes actually revive once it wears off again.
“The treatment slows down the release of nitrous oxide, it doesn’t stop it.”
Dr Officer’s research forms part of the national Nitrous Oxide Research program (NORP), which involves the GRDC, DPIV, DAFF, Queensland University of Technology, University of Western Australia, University of Melbourne, Cotton Community Catchments CRC, New South Wales Department of Industry and Investment, and the Queensland Department of Environment and Resource Management.
At Hamilton, the nitrous oxide release from the soil is measured using high-tech Perspex and steel gas collection chambers. These are fitted to a tuneable diode laser which constantly monitors the nitrous oxide concentrations in the 12 automatically closing chambers.
The chambers close 16 times a day for 30 minutes to collect the nitrous oxide gas. Carbon dioxide levels are also measured in the chambers, while remote sensors log the moisture and temperature of the soil.
At the end of each recording period the chambers automatically open to release the gas into the atmosphere. The chambers do not close when it is raining or when the air temperature is excessively high.
The chambers are shifted around the plot sites every two weeks so as to minimise disruption to the crops’ normal growing pattern.
Dr Officer’s trial will not only inform future farm management practices, but will also provide detailed data to the National Greenhouse Gas Inventory and the National Carbon Accounting System (NCAS) specifically for the HRZ in Victoria.
