Utilization rate of fertilizer N and dynamic changes of soil NO3--N in summer maize field in semi-humid area of Northwest China
半湿润地区农田夏玉米氮肥利用率及土壤硝态氮动态变化

A field experiment on manual loessial soil was conducted to study the dynamic changes of NO3(-)-N in soil profile, utilization rate of fertilizer N, and relationships between N application rate and soil residual N accumulation during the growth period of summer maize under different N application rates (0, 45, 90, 135, and 180 kg hm(-2)). The results showed that in the whole growth period of summer maize, the NO3(-)-N concentration in the soil profile was the highest in 0-20 cm layer, and increased with increasing N application rate. The NO3(-)-N concentration in 0-60 cm soil layer changed significantly, but no significant change was observed in 60-100 cm soil layer. In the growth season of summer maize, soil NO3(-)-N accumulation presented a fluctuated decreasing trend due to the N uptake by crop and the precipitation. The N utilization rate (NUR) increased with increasing N application rate when the application rate was less than 135 kg hm(-2), but tended to decrease when the application rate exceeded 135 kg hm(-2). With the increase of N application rate, the N agronomy efficiency (NAE) decreased but the N physiology efficiency (NPE) increased. There was a significant positive correlation between soil residual N accumulation and N application rate (R2 = 0.957**, n = 5). The grain yield under N application was significantly higher than that without N application (P <0.05), and there existed a significant positive correlation between grain yield and N application rate (R2 = 0.934**, n = 5). In our experiment, the optimal application rate of fertilizer N was 135 kg hm(-2), which could harmonize the relationship between economic benefits and environment.