Effects of Nitrogen Application on Nitrogen Use Efficiency of Spring Maize and Distribution of Soil Nitrate Nitrogen in Northwest Hebei Province

Field experiment was carried out to investigate effects of different nitrogen application rates on yield,nitrogen use efficiency of spring maize and distribution of soil nitrate nitrogen(NO-3-N) in Northwest Hebei province.The results showed that yield of spring maize increased with the increasement of N application rate,and yield,N use efficiency of spring maize decreased significantly when N application rate was higher than 225 kg/hm2.From before sowing to after harvest of spring maize,NO-3-N content in 0-90 cm soil layers showed the trends of continuously decreasing under zero N treatment,while NO-3-N content in 0-30 cm and 30-60 cm soil layers showed the trends of increasing first,then decreasing rapidly and in the end keeping stable,NO-3-N content in 60-90 cm soil layers showed the trends of increasing at late growth stage under N treatments.After harvest,NO-3-N content in 0-180 cm soil layers decreased in a wave-manner with increasing of soil depth,when N application rates were 300 kg/hm2 and 375 kg/hm2,NO-3-N content in 60-90 cm,120-150 cm and 150-180 cm soil layers was significantly higher than that under other N treatments.With the increase of N application rate,NO-3-N accumulation in 0-90 cm,90-180 cm and 0-180 cm soil layers showed increasing trend,NO-3-N accumulation in soil layers had high leaching risk on condition of high N application rate.Therefore,through fully analyzing effects of N application on yield and N use efficiency,with the consideration of environment risk of soil NO-3-N distribution,the reasonable N application rate of spring maize should be controlled at 195~225 kg/hm2.