Responses of nitrous oxide emissions from crop rotation systems to four projected future climate change scenarios on a black Vertosol in subtropical Australia

Black Vertosols of subtropical Australia emit large amounts of nitrous oxide (N₂O) to the atmosphere under fertilizer-applied grain cropping compared to other Australian cropping soils. N₂O emissions can be mitigated by either reducing fertilizer N inputs or altering crop rotation systems. In this study, the WNMM agroecosystem model was used to investigate the responses of N₂O emissions from four different crop rotation systems including canola-wheat-barley (T1CaWB), chickpea-wheat-barley (T3CpWB), chickpea-wheat-chickpea (T4CpWCp), and chickpea-Sorghum (T5CpS) under projected future climate change scenarios on a black Vertosol at Tamworth, New South Wales, Australia. In simulations of the twenty-first century under four different scenarios for atmospheric greenhouse gas concentrations, the annual N₂O emissions from the four cropping systems increased with greenhouse gas forcing of the climate. The annual N₂O emissions from T4CpWCp (with no fertilizer N application) were the most sensitive to climate change, with 14.3-61.9% increase compared with historic simulations of 1952-2014. The simulated T5CpS treatment (with a long fallow) kept the gross margin-scaled N₂O emissions below 1 g N per Australian dollar under all climate change scenarios. This suggests that the inclusion of a long fallow in a crop rotation system can slow down the pace of increasing gross margin-scaled N₂O emissions in response to climate change. Our simulation results also imply that legume rotations as mitigation options on N₂O emissions may not be resilient to the future changing climate even though they can greatly reduce N₂O emissions under the current climate.