Effects of different N rates on fate of N fertilizer and balance of soil N of winter wheat

The fate of N fertilizer and balance of soil N under winter wheat farming were studied using filed15N micro-plot.The results show that crop yield would not increase when the nitrogen application rate is above N 150 kg/ha.Apparent recovery efficiency and agronomic efficiency of nitrogen fertilizer are constantly decreased with increasing of rate of nitrogen fertilizer,while the trend of physiological efficiency is low-high-low.At lower N rate,more soil N is absorbed by winter wheat than that from fertilizer N,and the ratio of soil N absorption to fertilizer N absorption is decreased under high N application.After the harvest of winter wheat,26.7%-40.6% of fertilizer N is resided in 0-100 cm,and 17.4%-24.8% of fertilizer N is lost.With increasing of nitrogen fertilizer application,the total balance of soil N is from deficiency to surplus,and NO-3-N in the root zone soil is from consuming nitrogen to cumulating nitrogen before seeding.There is similar trend between two wheat varieties.