Hongtao Xing, Mark Richards, Guangdi Li, Rohan Brill, De Li Liu, Allison Blake, Deb Slinger
NSW Department of Primary Industries, Wagga Wagga NSW, Australia
Legume crops are one of key rotation components in agricultural systems, supplying nitrogen (N) to following crops and potentially increasing farm profitability. However, with the increasing atmospheric greenhouse gas concentrations, Australia will become warmer and dryer in the future. This greatly threatens Australian crop production and brings uncertain impacts on the profitability of adding legumes into non-legume crop sequences. In this study, we optimised the crop model, APSIM, using 4-year experimental data, collected in Wagga Wagga, New South Wales, Australia. The optimised model was then used to predict lupin biological N2 fixation (BNF) and the contribution of fixed N to the subsequent canola under historical and future climatic conditions in the rainfed cropping systems. The simulation results showed that, when there was no N fertilizer applied to canola in lupin-canola rotations, BNF increased about 3% by 2071-2100 under the higher greenhouse gas emission scenario, comparing to 1961-2000. This results in about 20% of increase in the contribution of lupin fixed N to the subsequent canola seasons (NC). However, these benefits will be reduced to zero when N fertilizer applied in canola seasons is over 40 kg N/ha for BNF and 60 kg N/ha for NC, respectively, by 2071-2100 for RCP8.5. This indicates that future climate change would enhance the N contribution of legume fixed N to subsequent crops only when the non-legume crops received lower N fertilizer in the legume added rotation cropping systems.