[Optimum nitrogen application rate to maximum yield and environment protection for winter wheat in Weibei dryland, China.].

To get the optimum nitrogen (N) fertilization rate which could guarantee wheat yield and protect environment, we examined wheat yield, N use efficiency, apparent N loss and soil N balance in Weibei dryland with a 3-year field experiment. The results showed that annual wheat yield increased and then decreased as N application rate increased in all the years with different annual rainfall, but the cumulative apparent N use efficiency significantly decreased. Higher yield and N use efficiency were obtained at the fertilization rate of 150 kg·hm. Residual nitrate-N concentrations significantly increased with the increases of N application rate. When the N application rate was between 75 and 150 kg·hm, the apparent N loss and loss rate were nearly the same, but if N application rate was higher than 150 kg·hm, the apparent loss and loss rate significantly increased. In conclusion, N application rate at 150 kg·hm in Weibei dryland could guarantee high yield and N use efficiency, and simultaneously maintain residual nitrate-N concentration and reduce apparent N loss.