Response of Spring Maize Grain Yield, Nitrogen Efficiency and Soil Mineral Nitrogen to Nitrogen Application

In order to increase crop production and reduce environmental pollution by nitrogen(N)fertilizer, a field experiment was carried out to study the effects of N application rate on spring maize grain yield, N use efficiency and temporal and spatial dynamics of soil mineral N(Nmin). The results showed that the yield of spring maize increased significantly with N application rate increasing, but once the rate exceeded 180 kg·hm-2, the yield began to keep stable or trend to decline. With increasing of N application rate, N agronomic use efficiency, N uptake efficiency, N partial productivity and N harvest index all decreased significantly, however, N apparent use efficiency and N physiological use efficiency both first increased and then decreased. From seedling stage to maturity of spring maize, NO3--N content in 0~60 cm soil layer showed a trend of increase-decrease-increase-decrease and keeping stable at the end, but in 60~120 cm soil layer showed a trend of in-crease at the late growing stage under N treatment. With increasing of soil depth, soil NO3--N content decreased in a wave manner, when N application rates were 240 kg·hm-2and 300 kg·hm-2, NO3--N content in 60~100 cm soil layer was significantly higher than that under other N treatments. With the increase of N application rate, NO3--N accumulation in 0~120 cm soil layer increased significantly, but once the rate exceeded 240 kg·hm-2, accumulated NO3--N in soil layer had high leaching risk. In view of grain yield, N utilization efficiency and environmental benefit, 179~209 kg N·hm-2was the reasonable N application rate for spring maize under the experimental conditions.