Nitrogen losses and greenhouse gas emissions under different N and water management in a subtropical double-season rice cropping system

Nitrogen non-point pollution and greenhouse gas (GHG) emission are major challenges in rice production. This study examined options for both economic and environmental sustainability through optimizing water and N management. Field experiments were conducted to examine the crop yields, N use efficiency (NUE), greenhouse gas emissions, N losses under different N and water management. There were four treatments: zero N input with farmer's water management (N0), farmer's N and water management (FP), optimized N management with farmer's water management (OPT_N) and optimized N management with alternate wetting and drying irrigation (OPT_N+AWD). Grain yields in OPT_N and OPT_N+AWD treatments increased by 13.0-17.3% compared with FP. Ammonia volatilization (AV) was the primary pathway for N loss for all treatments and accounted for over 50% of the total losses. N losses mainly occurred before mid-tillering. N losses through AV, leaching and surface runoff in OPT_N were reduced by 18.9-51.6% compared with FP. OPT_N+AWD further reduced N losses from surface runoff and leaching by 39.1% and 6.2% in early rice season, and by 46.7% and 23.5% in late rice season, respectively, compared with OPT_N. The CH₄ emissions in OPT_N+AWD were 20.4-45.4% lower than in OPT_N and FP. Total global warming potential of CH₄ and N₂O was the lowest in OPT_N+AWD. On-farm comparison confirmed that N loss through runoff in OPT_N+AWD was reduced by over 40% as compared with FP. OPT_N and OPT_N+AWD significantly increased grain yield by 6.7-13.9%. These results indicated that optimizing water and N management can be a simple and effective approach for enhancing yield with reduced environmental footprints.