Effects of Nitrogen Application Rate on Yield and Nitrogen Utilization of Winter Wheat under Straw Returning Condition in Guanzhong Irrigation Area

A field experiment with five treatments was conducted to study the nitrogen fertilization application rate of winter wheat in Guanzhong area under the straw returning condition,and winter wheat variety Xinong 979 served as material.The yield and the component factors of winter wheat,the nitrogen utilization rate,the contents of the nitrate nitrogen in the soil and the content of wheat protein under the different treatments were determined.With the amount of nitrogen fertilizer increasing,the grain yield of the wheat,biomass,1 000-grain mass and the spike number per hectare climbed up and then declined.Grain yield,biomass and spike number per hectare reached its maximum under the treatment of N262.5,however,the maximum of 1 000-grain mass reached its maximum under the treatment of N175.Nitrogen recovery efficiency and nitrogen fertilizer use efficiency decreased along with the increase of the nitrogen application rate,while the nitrogen harvest index showed the tendency by increasing then declining and reached the largest under the treatment of N175.Compared to the N0 treatment,the accumulation of nitrate nitrogen in soil in the treatments N262.5 and N350 improved significantly after wheat harvest.The content of wheat protein increased significantly with the increasing of N applied in the range of 0-262.5 kg/hm2.The optimum application rates of N fertilizer should be in the range of 175-262.5 kg/hm2 considering the local technology level and the climate.