Effects Of Surface Mulching On Water And Nitrogen Use Efficiency And Grain Yield Of Winter Wheat

The Loess Plateau is the main planting area of dryland winter wheat in China,the rainy season in this area is concentrated in the summer fallow period,and the winter wheat growth period is dry with little rain,which leads to unstable crop yield and low nitrogen use efficiency.Therefore,how to efficiently use limited rainfall in summer fallow period,improve water use efficiency in growth period and further improve nitrogen use efficiency is an urgent agricultural practical problem.Surface mulching can reduce soil water evaporation and increase soil water storage in summer fallow period.On the other hand,it can increase plant transpiration and promote the absorption and utilization of nutrients by crops.Therefore,coverage has become a common planting pattern in rain fed agricultural.In this study,winter wheat in Yongshou county,Shaanxi province,where is a typical rain fed agricultural area in the loess plateau,was taken as the research object,and the location experiment was conducted for five consecutive years.with no nitrogen fertilizer as the control(CK),on the basis of applying 150 kg/hm~2 pure nitrogen,farmers'model(NM),ridge-mulching and furrow-seeding(RM+FS),plastic mulching(PM),and straw mulching(SM)were set up,with a total of five treatments.The effects of different surface mulching on winter wheat yield,water and nitrogen utilization and physiological characters were studied.The main results obtained are as follows:(1)Different surface mulching can basically achieve the goal of stable yield and increase production in dry years in Weibei dry tableland.Compared with NM treatment,the yield of RM+FS treatment increased by 5.6%~15.7%in deficit years and the aboveground biomass of that increased by 14.5%~29.1%,which showed negative effects in flat water years,but it was not significant;The aboveground biomass and the yield of PM treatment increased by 11.6%~23.2%and 6.1%~18.5%for five consecutive years,respectively,SM treatment had no significant yield in 2013–2014(flat water year),and the yield increased by 9.0%~22.5%and the aboveground biomass increased by 11.4%~31.7%in other years.(2)Compared with CK,nitrogen application had no effects on nitrogen content in all organs except in the first season,and nitrogen content in all organs could be significantly increased in the last four seasons.Compared with NM,different surface mulching had no significant effects on nitrogen content of different organs in the first two seasons,and the grain nitrogen content in SM treatment increased by 17.3%in the third season.The grain nitrogen content in different surface mulching decreased by 9.5%~19.9%in the fourth season,the straw nitrogen content decreased by 25.0%~38.9%and the glume nitrogen content decreased by 28.3%~41.7%;the grain nitrogen content in different mulching treatments decreased significantly by 11.3%~24.3%in the fifth season.The difference of nitrogen content in different organs is extremely significant in different years.The amount of nitrogen carried out in the aboveground increased by 24.2~305%under fertilizer application treatment in five growing seasons compared with CK;and increased to different degrees in the first three seasons compared with NM,while it did not increase in RM+FS and SM treatments,but it decreased in PM treatments by 17.9%and 8.3%respectively in the second two seasons.(3)SM had a significant positive effect on the yield through efficient fallow efficiency;Although RM+FS treatment did not show high fallow efficiency,it also promoted the yield by using rainfall in growth period efficiently.PM combines the advantages of both,not only improving fallow efficiency,but also making use of rainfall in growth period to achieve its high-yield goal.(4)RM+FS decreased in flat water years because of excessive tillers in the early stage,resulting in too much density in the late stage,production reduction caused by relatively insufficient nutrient and moisture,and the nitrate leaching peak went down by near 40 cm during the summer fallow in flat water years,which made leaching risk higher;For many years,the residue of nitrogen fertilizer in FM treatment is lower,and the risk of nitrate leaching is extremely low.However,under the condition of 150kg/hm~2 nitrogen application,the status of nitrogen fertilizer deficiency will appear in continuous planting.The effect of SM on yield increase is significantly obvious,but nitrate leaching has exceeded 2 m after 150 kg/hm~2 of nitrogen was applied for five consecutive years,which is very risky.(5)Dfferent mulching treatments inhibited root activity of winter wheat at different growth stages to some extent,compared with FM,with it decreased in PM treatment by 14.8%~44.6%,decreased in SM by 12.9%~35.4%,and RM+FS had no significant effect;The nitrate reductase(NR)activity in different growth stages was not significantly influenced,but the nitrate nitrogen content in boot leaves was influenced to some extent,during jointing stage,it was significantly decreased by20.6%and 24.4%in the PM and SM treatments,and decreased by 18.6%~23.8%in flowering stage.Photosynthetic index of flag leaves such as chlorophyll has been inhibited in flowering and filling stages,and although the influence on net photosynthetic rate of boot leaves in flowering has not reached significant level,there is also a certain declining trend,with a decline of 5.5%~14.1%.