The CSIRO has published new research showing how nitrous oxide emissions (N2O) from grain cropping systems in Australia can be reduced. Studying N2O emissions in agriculture is important as they make a large contribution to Australia’s greenhouse gas emissions. For example:
-agricultural soils in Australia produce 55% of the N2O emissions;
-over 30% of N2O emissions are attributed to nitrogen fertilisers;
-70% of the 1 million tonnes of nitrogen fertiliser used every year in Australia is applied to cereals; and
-N2O emissions have been found to be higher in grain systems in subtropical and temperate zones of eastern Australian.
The research titled ‘[n]itrous oxide emissions from grain production systems across a wide range of environmental conditions in eastern Australia’ utilised the Agricultural Production sIMulator (APSIM) to identify N2O mitigation options that did not limit, but also improved grain yields under different climatic environments and soils in eastern Australia. The regions included in the study area were Kingaroy, Kingsthorpe, Tamworth, Wagga Wagga, Horsham and Hamilton. The simulations incorporated data from six field sites and found that using grain legumes in rotation with cereal crops was effective at mitigating N2O emissions (as less nitrogen fertiliser was required as a result of the legume nitrogen input). The simulations also showed the value of legumes as disease break crops for cereals further adding to its value. Further, even though N2O emissions were found to be higher in wet years (due to denitrification being higher in wet soils), as plant-available water is the main limiting factor for growth in Australian dryland cropping systems, less nitrogen fertiliser in needed in dry years as the plant growth is limited by the lack of water and therefore requires less nitrogen fertiliser.
The authors also noted that while they found that maximum wheat yields in monocultures were higher than when in rotation with chickpea (one of a number of legumes simulated), they cautioned this result as it did not agree with numerous previous studies. Additionally, the APSIM model had not included the value of legumes in controlling root diseases in cereals which could be a viable trade-off. The final mitigation strategy recommended was splitting nitrogen fertiliser application as the simulations showed that it had no effect on yield and reduced N2O emissions by up to 22% compared to single nitrogen fertiliser application, however this was only found in the southern region and made no difference in the northern region of the study area.
Research such as this is vital not just from the national impact level in reducing a damaging green-house gas but also at the farm-scale as it saves farmers money while having no impact on crop yield. Additionally, this is another example of research showing that legumes are a viable substitute for nitrogen fertilisers, making the soil more sustainable and in a climate such as Australia’s this can only be a good thing.
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