Why consider nitrous oxide from pastures?
Nitrous oxide is nearly 300 times more active as a greenhouse gas than carbon dioxide. Agriculture releases about 80% of Australia's nitrous oxide emissions. However, the total amount of nitrous oxide emissions in Australia is relatively low compared to the total of all greenhouse gas emissions.
Sources of nitrous oxide
Nitrous oxide emissions from the soil result from biological and chemical processes that use inorganic nitrogen compounds (ammonium, nitrite and nitrate). The processes that release nitrous oxide include microbial mediated nitrification in aerobic soils, denitrification of nitrate in anaerobic soils, nitrifier denitrification of ammonium and the chemical reduction of nitrous oxide and nitrate.
Benefits from reducing nitrous oxide emissions
Nitrous oxide has nearly 300 times the global warming potential of carbon dioxide. This means that avoiding the release of 1 tonne of nitrous oxide would be eligible to create nearly 300 carbon dioxide equivalent offset units. In the case of emissions resulting from the application of inorganic fertilisers, nitrous oxide emissions are calculated from the amount of nitrogen applied in fertiliser multiplied by emission factors.
Barriers to reducing nitrous oxide emissions
A methodology for dryland agriculture in Western Australia is yet to be approved. The financial benefit of avoiding nitrous oxide emissions has to be assessed in light of the operational costs of achieving the abatement (including the costs associated with administering any abatement scheme), the value of any increase in agricultural production and any reduction in fertiliser costs.
Western Australian research shows the opportunity for generating abatement credits from dryland cropping in lower rainfall areas is limited by comparatively low emission rates and the timing of emissions. This has been attributed to comparatively low nitrogen fertiliser application rates, slow decomposition of stubbles and low rates of microbial activity. Where it can be justified, nitrification inhibitors may reduce nitrous oxide emissions from intensive agriculture.
Options to reduce nitrous oxide emissions
Except in intensive systems and high rainfall areas, the reductions in nitrous oxide emissions with these management options are likely to be low:
- Use less nitrogen fertiliser. This only makes sense if more fertiliser is being added than is needed. Use soil testing and tissue testing, and visual signs to manage nitrogen fertilser rates.
- Use split applications of nitrogen fertilisers. This increases the efficiency of use by plants, allowing less nitrogen to be lost to the atmosphere or leach. This option is particularly suited to waterlogged sites.
- Use legume crops or pastures in the rotation instead of nitrogen fertiliser. More of the nitrogen is in the form of organic matter which is released more slowly and is used more effectively by growing plants. Calculate profitability of the options to make a financial choice.
- Use minimum tillage for cropping. This minimises organic matter breakdown and the release of nitrous oxide and nitrogen gas.
- Prevent waterlogging. Under waterlogged conditions, nitrate can be denitrified by soil bacteria to form nitrous oxide and nitrogen gas.
- Use nitrification inhibitors. These work by reducing nitrification which reduces nitrate leaching and the production of nitrous oxide. These inhibitors can be mixed with nitrogen fertilisers or applied separately. Check the efficacy with an agronomist before using this option.
For more information
Download Bulletin 4856 'Carbon farming in relation to Western Australian agriculture' (PDF 1.4MB).