Managing Global Resources for a Secure Future

Nitrous oxide (N₂O) emissions from Australian cropping systems are highly variable (e.g. emission factors from <0.5 to >5) due to the large variations in soil, climates and management practices under which crops are grown. Agricultural soils contribute 55% of national N₂O emissions, so mitigation of these emissions is important. In the present study, we explored N₂O emissions, yield and emissions intensity in a range of management practices in grain and sugarcane crops across eastern Australia with the Agricultural Production Systems sIMulator (APSIM). The model was initially evaluated against experiments conducted at six field sites across grain- and sugarcane growing regions in eastern Australia. Measured yields for all crops used in the experiments (wheat, barley, sorghum, maize, cotton, canola, chickpea and sugarcane) and seasonal N₂O emissions were satisfactorily predicted with R² values > 0.9. As expected, N₂O emissions and emissions intensity increased with increasing nitrogen (N) fertilizer input, whereas crop yields increased until a yield plateau was reached at a site- and crop-specific N rate. The mitigation potential of splitting N fertilizer application depended on the climate conditions and was found to be relevant only in the southern grain-growing region, where most rainfall occurs during the cropping season. Growing grain legumes in rotation with cereal crops has potential to reduce mineral N fertilizer requirements and so N₂O emissions. In sugarcane crops, slow release fertilizers showed potential for reducing N₂O emissions. Overall, N management strategies that maximize yields and increase N use efficiency showed the greatest promise for N₂O mitigation.