Effect of Nitrogen Fertilizer Rate on Photosynthetic Rate and Photochemical Efficiency of Flag Leaf,Grain Yield and Protein Content of Winter Wheat

A field experiment was conducted on high-yielding conditions to evaluate the effects of nitrogen fertilizer rate on changes of photosynthetic rate and photochemical efficiency in flag leaf,changes of sucrose content in flag leaf and grain after anthesis,and grain yield and protein content of winter wheat.The application of nitrogen fertilizer would increase photosynthetic rate and photochemical efficiency of ΦPSⅡ in flag leaf during the mid and late filling stage,increase the ratio of Fv/Fm at the end of grain filling stage.With the application of excessive nitrogen,the photosynthetic rate do not increase and photochemical efficiency of ΦPSⅡ decrease.The application of nitrogen fertilizer would increase sucrose content in flag leaf and promote sucrose supply in grain during early filling stages.During late filling stages,the nitrogen application at high rate would increase the amount of sucrose left in flag leaf,so the differences of sucrose content in grains among treatments of different nitrogen application rate were not significant.Compared with no nitrogen applied,the nitrogen application rate at 105～195 kg·ha~(-1) increased grain yield significantly and the nitrogen application rate at 105～240 kg·ha~(-1) increased protein content significantly.When the nitrogen application rate increased to 285 kg·ha~(-1),grain weight,grain yield and protein content decreased.With the yield and protein content were concerned,the nitrogen application rate at 105～240 kg·ha~(-1) was recommended.