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 carriedout 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 exceeded180 kg·hm-2, the yield began to keep stable or trend to decline. With increasing of N application rate, N agronomic use efficiency, N uptakeefficiency, N partial productivity and N harvest index all decreased significantly, however, N apparent use efficiency and N physiological useefficiency both first increased and then decreased. From seedling stage to maturity of spring maize, N03-N content in 0-60 cm soil layershowed a trend of increase-decrease-increase-decrease and keeping stable at the end, but in 60一120 cm soil layer showed a trend of in-crease at the late growing stage under N treatment. With increasing of soil depth, soil N03-N content decreased in a wave manner, when Napplication rates were 240 kg·hm-2 and 300 kg·hm -2, N03-N content in 60-100 cm soil layer was significantly higher than that under otherN treatments. With the increase of N application rate, N03-N accumulation in 0-120 cm soil layer increased significantly, but once the rateexceeded 240 kg·hm-2, accumulated N03-N in soil layer had high leaching risk. In view of grain yield, N utilization efficiency and environ-mental benefit, 179-209 kg N.hm-2was the reasonable N application rate for spring maize under the experimental conditions