Yield and nitrogen use efficiency of winter wheat with different soil fertility

Both the existing soil fertility and fertilizer application have important influences on crop yield and nitrogen (N) use efficiency, but knowledge about their interaction is still lacking. The interaction of N application and integrated soil fertility index on grain yield and N fertilizer use efficiency such as N recovery efficiency, soil N dependency rate, and N contribution rate of wheat was studied through 2-year in situ tests in Changshu County of the Taihu Lake region, China. The results indicated that there are desirable quantitative relationships among the assessment indices, N application level and integrated soil fertility index. The regression coefficients showed that the ratio of the relative contribution of soil fertility and N application level to wheat yield was 0.48:1, and their contribution ratios to fertilizer N utilization efficiencies were 1.10:1, 1.45:1 and 1.93:1, respectively. The effects of both soil fertility and N application level on yield and N recovery efficiency indicated that it is difficult to simultaneously improve yield and N recovery efficiency of wheat by improving soil fertility when attempting to maximize yield. Only by enhancing soil fertility, reducing the N application level and decreasing the maximum yield, can high levels of N recovery efficiency be achieved. For this study, a ratio of N application level decrement to integrated soil fertility increment greater than 0.89 was necessary to increase the N recovery efficiency to 55%. Under this optimal condition, the reduction in N application level was 16%, and the mean yield loss of wheat was only 8%.