Effects Of Nitrogen Fertilizer On Winter Wheat After Maize Straw Returning In Guanzhong Plain

Guanzhong Plain is a typical winter wheat-summer maize rotation region, where the straw incorporated into the soil has become a common agricultural practices. Two field experiments were conducted for optimizing nutrient management and improving the utilization rate of fertilizer. The experiment was arranged in a split block design with two main treatments and five subplots. The main treatments included all the maize straw return to soil and all straw removal treatment, and the subplots were five N application rates of 0, 84, 168, 252 and 336kg/hm2 with four replicates. In order to provide scientific basis for optimizing nitrogen management under straw return condition, we analysised the effect of straw returning on winter wheat growth, yield and soil nutrient changes. Main conclusions were as follows:1. The long-term location test which lasted 3 years was located in Zhouzhi County of Shaanxi Province. During the three years, the two curves of fertilizer response equation that straw returning or clean tillage intersected at 153kg/hm2(2011-2012) 187kg/hm2(2012-2013) and 99kg/hm2(2013-2014) respectively. The yield of winter wheat increased when N application rate is higher than the critical value after straw returned to soil. The yield of winter wheat decreased when N application rate is lower than the critical value after straw returned to soil. The intersection points(critical values) of biomass were 190 kg/hm2(2011-2012), 202 kg/hm2(2012-2013) and 102 kg/hm2(2013-2014) respectively.2. The average of the 0-20 cm SOM increased by 6%(relative value) and 20-40 cm increased by 12% after 3 years straw returning. Straw returning can increase the nitrate nitrogen residue of topsoil after the wheat harvest. During the three years, the nitrate nitrogen remaining amounts in the plough layer soil was 27.6%, 5% and 4.8% higher than clean tillage treatment after the wheat harvest respectively. There is no significance in soil available phosphorus. Straw returning can increase the content of available potassium about 9.2%.3. Straw returning increased NUE by 7.1%~25.4% than clean tillage. With the increase of N rate, the potassium harvest index had different degrees of reduction and the straw returning decreased 1%~3.4%, and the single nitrogen decreased 1.8%~4.7%. Nitrogen fertilizer with the straw returning can increase the content of nitrogen by 14.6% to 18.5% in grain and increased by 12.7%~19.2% of clean tillage.4. The other experiment site is in Wugong County of Shaanxi Province. The result shows that straw returning was increased winter wheat yield when N rate higher N than 79kg/hm2 and decreased when N rate lower than 79 kg/hm2. There was no significantly different on basic seedlings and tiller number before winter among all treatments. There is a trend that spring tiller number first increased and then decreased again increased with the increase of nitrogen application. There is no significant different on spring tiller number under different nitrogen levels. The high fertilizer( 252 and 336 kg/hm2) of clean tillage is significantly higher than those of the low nitrogen treatment of clean tillage. N rate on winter wheat grain number and grain weight were not significantly different. There is a trend that ears of winter wheat first increased and then decreased with the increase of nitrogen application. There is no significant difference that the content of nitrogen and straw to grain and shoot nitrogen phosphorus and potassium. There was no significant difference in winter wheat seedlings and tiller number before winter under the condition of same N application rate. Straw returning can reduce spring ineffective tillers and increase effective panicles of winter wheat. NPK contents of winter wheat were not significantly affected by whether straw returning or N application rate.