Effect of N Fertilizer Rate on Fate of Labeled Nitrogen and Winter Wheat Yield on Different Soil Fertility Fields in Chao Soil Area in North Henan

To provide evidence for optimized N fertilizer management of current winter wheat(Triticum aestivum L.) production,effects of N fertilizer rate on the fate of labeled nitrogen and wheat yield were studied with both field plot experiment and 15N labeled micro-plot experiment in Chao soil in north Henan with high fertility and medium fertility field respectively.The results showed that 17.43%～38.75% N accumulated in wheat plant at harvesting was derived from N fertilizer applied,and 61.25%～82.72% from soil.The ratio of the fertilizer N accumulated in plant to the total plant N was more in high fertility soil than that in medium fertility soil,but the ratio of soil N accumulated in plant to the total plant N was less in medium fertility field than that in high fertility field.With the increase of N fertilizer rate,the amount of fertilizer N accumulated in plant increased,the amount of fertilizer N remained in soil and lost from soil also improved,whereas excessive fertilization would inhibit the amount of soil N accumulated in plant;the N fertilizer recovery rate,N fertilizer residual rate and N fertilizer loss rate were 25.51%～40.77%,20.30%～47.14%,17.75%～48.69% respectively,with the first two index were less in high fertility field than in medium fertility field,but not with the third index.With the increase of N fertilizer rate,the ratio of risk/benefit of applied fertilizer N improved,which exceeded 1 when N fertilizer amount applied reached 270 kg/hm2.With the increase of N fertilizer rate,the ratio of N fertilizer remained in 0~20cm layer to 0~100cm soil decreased,but the ratio of N fertilizer remained under 20cm layer to 0~100cm soil increased,fertilizer N move down obviously in medium fertility field.N fertilization was in favor for wheat yield increase,the N fertilization rate for best yield in high fertility field was less than in medium fertility field.