Effect Of Decreasing Nitrogen Rate On Wheat Yield And Nitrogen Use Efficiency And Selecting High Nitrogen-use-Efficiency Wheat Cultivars

In view of current situation of increasingly scarce water resources in Hetao irrigation area and serious fertilizer waste in the wheat production,based on the water-saving irrigation mode established by the previous study and conventional application amount of fertilizer by the farmer,different reduced application of nitrogen was used for studying the relationship among growth and development of spring wheat,photosynthetic characteristics,substance accumulation,yield formation and utilization of water and fertilizer systematically,disclosing physiological mechanism of efficient utilization of nitrogen fertilizer on the water saving condition deeply and defining the nitrogen application range of realize high yield of spring wheat and high utilization efficiency of water and fertilizer.In addition,in the water-saving irrigation mode,the differences in morphological characteristics,economic yield and nitrogen utilization of different varieties of spring wheat were compared and studied and the nitrogen efficiency variety suitable for plantation in Hetao irrigation area was screened.The main finds were as below:1.On a basis of the conventional nitrogen application by farmers,the amount of nitrogen fertilizer was reduced gradually.The measured economic yield showed a partial unimodal curve declining trend,and there were significant differences among the number of spikes,the kernels per spike,and different amount of nitrogen applied to the economic yield,but there was no significant difference in 1000-grain weight.In these two irrigation modes,with the decrease of nitrogen fertilizer application amount,the nitrogen content of plant,nitrogen accumulation amount,apparent utilization ratio of nitrogen and agricultural efficiency of nitrogen all showed partial unimodal curve declining trend,the partial productiviy of nitrogen fertilizer and physiological efficiency of nitrogen showed a linear increase trend.The apparent utilization ratio of nitrogen,agricultural efficiency of nitrogen fertilizer and physiological efficiency of nitrogen showed negative correlation with the partial productivity of nitrogen fertilizer and nitrogen application amount.The optimal nitrogen application amount(pure N)for spring wheat in the water saving irrigation mode of Hetao irrigation area to achieve high yield and high nitrogen efficiency was 112.7 to172.2 kg/hm~2.Where,20%of it was used as seed fertilizer and 80%of it was dressed before the jointing.2.In two irrigation modes,with the decrease of nitrogen application amount,the plant height of wheat florescence,the length,width and area of the top three leaves showed declining trend,but there was no obvious change in the stem diameter;under appropriate reduced application of nitrogen,the SPAD value of flag leaf,photosynthetic rate,water utilization efficiency(WUE),Fv/Fm behaved high,but the transpiration rate was relatively low.In the water-saving irrigation mode,the LAI and LAD in the later growth period of wheat under the reduced application of nitrogen declined slowly,the high value duration was long,colony growth rate(CGR)was faster,and the volume of kernel and grain filling rate 20d after flowering was obviously higher than that in conventional irrigation mode.3.In two irrigation modes,there were significant differences in the plant morphology,nitrogen utilization and yield characteristics of different varieties of wheat.Through clustering analysis,two high yield and high nitrogen efficiency varieties like Yongliang 4#and La 07-0145 were screened and suitable for application to the water-saving irrigation mode of wheat in Hetao irrigation area.The common features showed that high plant height,large leaf area of single plant,many kernels per spike,moderate grain weight,high nitrogen utilization efficiency and high economic yield.