Effect Of Nitrogen Fertilizer Application On Winter Wheat Growth And Law Of Maize Straw Decomposetion Under Maize Straw Returning In Guanzhong Irrigation Area

As one of the main rotation system management in Guanzhong irrigation area Winterwheat-summer corn rotation system was been cooperated with straw returning, and thismeasure has very important meaning to promote winter wheat yield in Guanzhong irrigationarea. Nitrogen fertilizer has crucial effect on wheat yield and quality, however, unreasonableapplication of N fertilizer may not only cause lower grain yield and quality, as well asenvironmental degradation; eventually restrict the sustainable development, high output andefficiency of agriculture production. Two years field experiment(six treatments on thecondition of straw residue return amount of nitrogen application as0,87.5,175,262.5or350kg/hm~2respectively and175kg/hm~2without straw residue return for the first season andnitrogen application as0,84,168,252, or336kg/hm~2, each plot split into two sub-plot undermaize straw returned or removed for the second season) was conducted to investigate theeffect of nitrogen application cooperated with maize straw returning on winter wheat yield,nutrition absorption，nutrient of cultivated soil layer. What’s more, Nylon mesh bags methodwas used to study on the decomposing process of maize straw residue and the prosperity ofdry mass, nitrogen, phosphorus and potassium releases from maize straw residue during thewinter wheat grown season under field circumstance. The results are as follows:(1) Compared with no stover incorporation treatments, wheat yield of the stoverincorporation plus nitrogen applications (N+S) treatments show a trend of increasesignificantly by18.5%in the first season while decrease when the nitrogen application rate islower than168kg/hm~2and increase when the nitrogen application rate is higher than168kg/hm~2in the second season, but the difference is not significant. The precipitation of thesecond year is higher than the first year，the function of keep soil humidity by straw residue isnot work in the second. This is a main reason for the yield is not as significant increase as theyield of first year.(2) With the increase of nitrogen application rate, nitrogen content of wheat grain leafand glume in the S+N treatment increased significantly in both season; however the effect ofmaize stover returning on P and K content of aerial part of winter wheat have shown different pattern in different season. Nitrogen fertilizer use efficiency and agronomic nitrogen useefficiency in N+S treatments were higher than those of only nitrogen fertilizer was applied(N)treatments by17.77%and66.76%(2010-2011);3.29%~24.46%and15.04~30.05kg/kg（2011-2012）.(3) Compare with control, soil SOM in treatments of N+S have a trend of increase by0.22%~11.90%; compare with the N treatments, the N+S treatments have a trend of increasenitrate nitrogen amount in the cultivated soil layer by-0.6%~74.1%, and have a potential ofkeep nitrate nitrogen stay at the cultivated soil layer, but this difference is not significant.What’s more, the N+S treatments can keep soil available K of the cultivated soil layer at ahigher level than the N treatments with a increase of0.74%~17.87%.(4) Soil water use efficiency of N+S treatments shown a6.92%average increase than Ntreatment, and this trend is increasing by the increasing of soil layer depth. Crop water useefficiency and precipitation efficiency of the N+S treatments had shown an average increase5.14%and1.18%respectively.(5) After190days decoposition period, maize stover decoposition has experienced3period during winter wheat growing season. Dry mass of maize stover has shown a higherdecomposed speed in first40days, followed by a low decomposed speed during the periodfrom40thto70thday, and then another higher decomposed speed appear during the periodfrom70thto190thday. The proportion of Maize stover dry mass decomposed amount in abovethree period of total decomposed amount is59.12%,1.06%,39.83%in Control treatment(CK)and58.98%,7.07%,33.96%in nitrogen fertilizer treatment(NF). After the whole experimentalperiod, the proportion of maize stover decomposed amount is28%~30%. Among three mainnutrient element, the realse rate of K from maize stover is the biggest one, N take the secondplace and P is the smallest one with the realse rate as79.41%,38.10%and37.28%. Comparewith CK，NF has shown a trend of increase the decompose rate and N and P release rate, butthe difference is not significant.