The optimized nitrogen rate reduced ammonia emissions from rice paddies in the cold region of Northeast China

Abstract

Ammonia (NH₃) volatilization is a main pathway of nitrogen (N) loss from rice (Oryza sativa L.) paddies, which results in lower N use efficiency (NUE) and greater risk of environmental pollution. Excessive N fertilization has a negative effect on yield sustainability and NUE to varying degrees. NH₃ emissions are affected by many factors, and the climatic conditions and planting patterns of rice fields in Northeast China are different from those in other regions, resulting in the specificity of NH₃ emissions in this region. The current two-year field experiment studied the effects of different N application levels, 0, 75, 105, 135 and 165 kg N ha⁻¹, on NH₃ emissions and the related factors affecting NH₃ volatilization loss and their relationships. The results demonstrated that the loss of NH₃ from volatilization and the ratio of NH₃ volatilization to N application increased with increasing N fertilizer application. The NH₃ losses resulting from basal N fertilizer, first N topdressing and second N topdressing accounted for 35.29–59.59 %, 29.32–59.66 % and 3.08–26.49 %, respectively, of the seasonal cumulative NH₃ volatilization. The seasonal cumulative NH₃ volatilization from the N application treatments accounted for 0.32–0.64 % and 1.84–2.40 %, respectively, of the applied N fertilizer. The main factor influencing NH₃ volatilization was the surface water ammonium-N (NH₄⁺-N) concentration (p<0.01); precipitation inhibited the volatilization of NH₃, and surface water pH fluctuated the least. There was a linear plateau between yield and N application, and a quadratic relationship between NUE and N application. Compared with the N135 and N165 treatments, lower N application increased NUE and significantly reduced NH₃ volatilization losses while maintaining yield. Our research revealed that an appropriate decrease in N fertilizer application in Northeast China paddy fields could meet agronomic and environmental goals, and the appropriate N fertilizer application rate for our experiment was approximately 125 kg N ha⁻¹.