Nutrition Mechanism And Environmental Effects Of Increasing Wheat Yield By Low N Input And Plastic Film Mulching In Dryland

Plastic film mulch cultivation is widely applied across the world due to the good soil hydrothermal conditions and the effect of improving crop yield.Nitrogen（N）fertilizer input can improve the crops yield,but long term N overfertilization widely exists in dryland,and the effects of long term overfertilization has resulted in a large amount of nitrate-N accumulation in soil and increasing the risk of environment pollution by nitrate.Therefore,the research on how to regulate the N input to increase winter wheat yield and reduce the risk of environment pollution by nitrate under plastic film mulch is important to the sustainable development of agriculture systems in dryland.A three-year winter wheat field experiment with plastic film mulch plus different N application rates was carried out in Loess Plateau to study the nutrient translocation and utilization of winter wheat,and the effects of improving winter wheat yield by reduced N input and plastic film mulch on the risk of nitrate pollution.The main results obtained were as follows:（1）Plastic film mulch（PM）improved the winter wheat yield,aboveground biomass and aboveground N,P,K accumulation,but it significant decreased grain N content.Increased N input appropriately could increase winter wheat grain yield and N content.Compared with no mulch（NM）treatment,winter wheat grain yield was significantly increased by 13%due to the significant increase of spike number by15%.Plastic film mulch significant increased winter wheat aboveground biomass by 14%and resulted in significantly increasing the aboveground N,P,K accumulation by 14%,25%,20%,respectively.Plastic film mulch significantly decreased the winter wheat grain N content of 2 g kg^-1.However,the grain N content could be improved by increasing N input under plastic film mulch condition.So,both high grain yield and high quality grain could be achieved by increasing N input in dryland under plastic film mulch condition.（2）Plastic film mulch significantly increased aboveground N,P,and K accumulation at winter wheat anthesis and N,P,and K translocation after anthesis.The grain N,P,and K nutrients were mainly contributed to the translocation of N,P,and K after anthesis.Plastic film mulch and N input had no significant effects on grain N,P,K uptake after anthesis.Increasing N input appropriately could improve the N,P,and K translocation after anthesis under plastic film mulch,which could provide the chance to achieve both high wheat yield and high grain quality in dryland.Compared with no mulch,PM increased the aboveground biomass by 19%at winter wheat anthesis,thus increased the aboveground N,P,K accumulation by 20%,27%,25%,respectively,and N,P,and K translocation after anthesis by 15%,27%,27%,respectively.However,plastic film mulch had no effect on grain N,P,and K uptake after anthesis.Increased N input had significantly affected winter wheat N,P,and K translocation after anthesis.,with an increased trend.（3）Plastic film mulch significantly increased winter wheat water use efficiency and precipitation use efficiency.The main reason for this was the significant increase of grain yield.Soil nitrate-N accumulation at 0-200 cm soil layer was not significant different under both cultivations,which was due to the higher N uptake of wheat under plastic film mulch and higher soil nitrate-N leaching under no mulch.There was a large amount of nitrate-N accumulated in soil under both cultivations.The effective practice to mitigate nitrate N residues is to reduce N input under both cultivations.Compared with no mulch,plastic film mulch had no significant effects on average annual water consumption.However,as for each year of water consumption,plastic film mulch decreased water consumption by 9%in 2016and increased water consumption by 17%in 2017.Plastic film mulch significantly increased wheat water use efficiency by 13%,as well as increase of precipitation use efficiency by 14%.Plastic film mulch significant increased soil nitrate N content at 0-20 cm soil layer.Compared with the beginning of experiment,three-year plastic film mulch increased soil available P at0-20 cm soil layer,but had no significant effects on soil available K.In conclusion,to prevent the nitrate N lost to the environment,we could reduce N input,but should pay more attention to the grain N content.Therefore,an appropriate N fertilization rate is important for the wheat production under plastic film mulch in dryland.