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...