Nitrogen management to reduce GHG emissions while maintaining high crop productivity in temperate summer rainfall climate

Nitrogen (N) fertilizer management determines the productivity and environmental footprint of intensive wheat-maize double-cropping systems in the North China Plain (NCP). The N fertilizer application rate can be optimized by balancing the trade-off between crop productivity and N2O emissions. Applying more N fertilizer to wheat in the dry, cool winter season while less N to summer crops is expected to reduce the N2O emissions without scarifying yield, because summer crop (maize) will use the residual N fertilizer from the previous crop season (wheat) to maintain their productivity. We combined four years of experimental data and soil-plant system modeling to assess the productivity and greenhouse gas emissions resulting from various N fertilizer management strategies. The farming systems model APSIM was used to simulate the wheat-maize double cropping system with N fertilizer application rates of 0–920 kg N ha−1 yr−1. The APSIM model explained 93% variation in biomass (RMSE = 0.88), 82% variation in soil mineral N (RMSE = 34.1), and 70% variation in N2O emission (RMSE = 1.37) measured in the experiment. The default IPCC emission factor (0.5% for the wheat season and 1.6% for the maize season) underestimated the N2O emission by 7.25 kg ha−1 when the local N fertilizer rates were applied (about 325 kg N ha−1 for wheat and 257 kg N ha−1 for maize). A N rate of 420 kg N ha−1 yr−1 would reduce GHG emission to the minimum (1.15 t CO2-eq ha−1 yr−1) while achieving more than 90% of the maximum grain yield. Additionally, allocating more N fertilizer to the wheat crop, while reducing the N fertilizer input for maize, did not significantly change grain yield of either crop, but further reduced net GHG emission by 1.07 t CO2-eq ha−1 yr−1. The APSIM model describes the crop growth and soil N dynamics of a wheat-maize double cropping system that receives N fertilizer at rates up to 920 kg N ha−1yr−1. The site-specific modeling results indicate that appropriate N fertilizer management, i.e., adjusting the rate and time of N applications, can lower the net GHG emission without impacting crop yields. Our study provides a practical and reliable method to develop a "win-win" strategy for N fertilizer management in double-cropping systems.