Studying The Effects Of Different Mulchingpracticesduring The Summer Fallow Undernitrogenfertilizer Reduction Onwinter Wheat Yield Increase Indryland

Winter wheat is the main cereal crop on the Loess Plateau,and drought is the typical feature of the Loess Plateau.Rainfall in this area is not only limited,but also varies greatly over seasons and years.Two thirds of the rainfall mainly occurs in summer months from July to September,these three months are the summer fallow period of winter wheat.If the precipitation during the summer fallow can be kept to the greatest extent,it will be able to significantlyimprove the pre-sowing soil moisture of winter wheat,which plays an important role in the high yield of winter wheat in dryland.In addition,farmers in this region are blindly pursuing high yield of winter wheat and applying excessive nitrogen fertilizer,so that a large amount of nitrate-N is remained in the soil after winter wheat harvest,which not only causes a large amount of nitrate-N to be lost by leaching along with water,but also causes great environmental problems.Therefore,in this study,winter wheat was taken as the research object in Yujiagong Village,Yongshou County,Xianyang City,Shaanxi Province.Mulching during the summer fallow is carried out on the basis of reducing nitrogen fertilizer application.No-nitrogen control?CK?without nitrogen fertilizer application,farmers'conventional treatment with applying pure nitrogen 195 kg ha^-1?FM?,and farmers'nitrogen reduction treatment with applying pure nitrogen 150 kg ha^-1?FRM?were set up,in addition,ridge-film and furrow-straw mulching during the summer fallow?SFRM?,plastic film mulching during the summer fallow?SFPM?and straw mulching during the summer fallow?SFSM?were set up on the basis of applying pure nitrogen 150 kg ha^-1.A total of six treatments were carried out to study the effects of nitrogen reduction combined with mulching during the summer fallow on water use,nutrient uptake and winter wheat yield in2017-2018 and 2018-2019.Through the two-season experiment,the main results we have obtained are:1. Compared to FRM,FM tended to increase the winter wheat yield and yield components,but the difference was not significant.It shows that the nitrogen fertilizer application with 150 kg ha^-1 in this area can meet the demand of winter wheat growth and achieve the purpose of stabilizing winter wheat yield.It is feasible to reduce the nitrogen fertilizer application.Moreover,reducing nitrogen fertilizer application combined with mulching the soil surface during the summer fallow could be able to achieve the purpose of increasing winter wheat yield,and SFSM had the most significant effect.Compared to FRM,the average yield associated with SFSM increased 852 kg ha^-1.Compared to FM,the average yield associated with SFSM increased 792 kg ha^-1.2. Compared to FM and FRM,the three mulching treatments during the summer fallow can increase the soil water storage in 0-200 cm soil layers before sowing and after harvest,and are more conducive to increase the soil water storage in 80-200 cm soil layers,among which SFSM had the best water storage effect.Nitrogen fertilizer application and mulching during the summer fallow can increase the water consumption during the winter wheat growth period,and the effect of SFSM is the best.Except that the difference between SFSM and SFPM was not significant,the differences between SFSM and other four treatments were significant.3. Compared to CK,nitrogen fertilizer application and mulching during the summer fallow can both significantly increase the grain,straw and glume nitrogen concentration.Compared to FM and FRM,the three mulching treatments during the summer fallow tended to reduce the grain,straw and glume nitrogen concentration.Compared to FRM,SFRM and SFPM tended to reduce aboveground N uptake,whilst SFSM tended to increase aboveground N uptake.Compared to FM,FRM and the three mulching treatments during the summer fallow all improved nitrogen use efficiency,nitrogen agronomic efficiency and nitrogen physiological efficiency.4. Compared to CK,nitrogen fertilizer application and three mulching treatments during the summer fallow had no significant effect on P concentration and P uptake of various organs.Compared to CK,nitrogen fertilizer application and three mulching treatments during the summer fallow tended to decrease grain K concentration,whilst increase straw and glume K concentration.5. Compared to CK,both FM and FRM significantly increased soil nitrate-N content and mineral-N content.Moreover,compared to the FRM,FM also significantly increased soil nitrate-N content and mineral-N content.Compared to the FM,the three mulching treatments during the summer fallow tended to decrease nitrate-N content and mineral-N content in the soil before sowing.However,compared to the FRM,the three mulching treatments during the summer fallow tended to increase nitrate-N content and mineral-N content in the soil before sowing,and the SFSM increased most.Compared to FM,the three mulching treatments during the summer fallow all significantly decreased nitrate-N content and mineral-N content in the soil after harvest.Based on the study of winter wheat yield,nutrient uptake,nitrogen residue in the soil after harvest and nitrate-N leaching risk,it can be concluded that the optimal application amount of nitrogen fertilizer is 150 kg ha^-1,and reducing nitrogen fertilizer application is feasible.Considering the effects of different mulching treatments during the summer fallow on water use,nutrient uptake and winter wheat yield,SFSM has the best effect and is suitable for popularization and application in Northwest dryland wheat production areas.