Effect of different levels of nitrogen on physiological characteristics of flag leaves and grain yield of wheat

The effects of different levels of nitrogen on wheat(Triticum aestivum) growth and development,on nitrogen use efficiency,on reducing the effects of excessive application of fertilizer on environmental pollution,and to increase crop yields were assessed using Yumai 49-198.The experiment was carried out at the experimental farm of Henan University of Science and Technology using nitrogen treatments of 120 kg/ha,180 kg/ha,240 kg/ha and 300 kg/ha.Plant response was measured in terms of photosynthetic rate,malondiadehyde(MDA) content,soluble sugar content,proline content,soluble protein content and superoxide dismutase(SOD),catalase(CAT) and peroxide enzyme(POD) activities in wheat leaves after heading.Increasing nitrogen within a certain range significantly increased photosynthetic rate,soluble sugar content,proline content,soluble protein content and SOD,CAT and POD activities,but MDA content decreased.When nitrogen exceeded a certain level,there was no obvious change in any of the indexes.With a nitrogen level of 240 kg/ha,the photosynthetic rate,soluble sugar content and other physiological indexes reached a maximum,so this was the optimum of the four nitrogen levels,for growth and yield increase of wheat.