Changes Of Winter Wheat Yield And Soil Fertility Under Long-term Straw Management And Nitrogen Application

Guanzhong Plain is the main grain production area in Shaanxi Province,where wheat straw with high stubble and summer maize straw return to soil directly become one of the routine agricultural measures.In order to provide the scientific basis for the high yield,high efficiency and improvement of soil fertility under winter wheat-summer maize rotation systerm in Guanzhong Plain,A long-term fixed site field experiment was conducted in Zhouzhi county.The experiment was arranged in a split block design with two main treatments and five subplots.Full straw return of maize(S+N)and no straw return(N),in main plots,and five chemical nitrogen treatments 0,84,168,252and 336 kg N/hm~2,as sub-plots.The main results are as follows:1.Through the analysis of the nitrogen fertilizer effect curves,with the year shifting backwards,except for 2016 and 2017,regardless of whether the straw was returned to soil or not,the nitrogen fertilizer rate corresponding to maximum wheat yield was gradually reduced,and the maximum wheat yield was higher in straw return treatments than in no straw return treaments.From 2012 to 2016,the two effective curves of N fertilizer that straw returning and straw removal intersected at 153,187,76.5,99and 147 kg N/hm~2 respectively.When the nitrogen fertilizer rate was lower than the intersection point,the yield of wheat was lower in straw return treaments than in no straw return treaments.On the contrary,the yield of wheat is higher in straw return than in no straw reurn treaments.2.The number of spikes and grains per spike were the main factors that affected the yield of winter wheat under the condition of straw return and nitrogen fertilizer application.The effects of nitrogen application rate and interannual climatic conditions on grain yield,panicles,1000-grain weight and harvest index were greater than the effect of straw return.The interaction effect between two factors on the number of grains per spike was not significant,the straw×Nitrogen rate interaction effect on grain yield was significant,but the straw×Nitrogen rate interaction effect on other factors was not significant.Interaction effect of straw returning and interannual climatic conditions had a significant effect on panicle number,but had no significant effect on other factors.3.Soil microbial biomass carbon,nitrogen and dissolved organic carbon can be used as an indicator to evaluate the quality of soil fertility.Because labile carbon and nitrogen were affected by many factors such as temperature,soil moisture,fertilization,crop absorption and straw decomposition during the growing season of wheat,showing regular fluctuations.With time soil microbial biomass carbon decreased from tillering stage to wintering stage,then increased until jointing stage and declined later.And soil dissolved organic carbon increased from tillering stage to jointing stage and decreased later with time,the dynamic change of soil microbial biomass nitrogen in the whole wheat growing season showed a decreased trend.4.Compared with no straw return treatments,straw returning significantly increased the microbial biomass carbon and dissolved organic carbon in the soil,and increased by 6.7%and9.3%in average,respectively.Microbial biomass nitrogen in straw return treaments were higher than no straw return traements,but significantly increased only in jointing stage and maturity stage.With the increase of nitrogen rate,microbial biomass carbon and nitrogen significantly decreased.While with the increase of nitrogen rate,dissolved organic carbon significantly increased in straw return treatments,and increased by 11.8%in average,but the dissolved organic carbon in no straw return treatments showed a increased trend first and declined later.Overall,straw returned can obviously increase soil microbial biomass carbon,nitrogen and dissolved organic carbon,and the application of chemical nitrogen fertilizer promoted the decomposition of maize straw,but excessive application of chemical nitrogen fertilizer decreased the microbial biomass carbon and nitrogen,and will have negative effect on the growth of microorganism.5.The content of soil organic matter,nitrate nitrogen,available phosphorus and available potassium in straw return treaments were higher than in no straw return in the 0-40cm soil layer,but the difference between two treaments were not significant.The soil organic matter content had a increased trend after long-term straw return,as the number of years increased soil organic matter increased year by year.But the content of nitrate nitrogen,available phosphorus and available potassium in all soil layers were not increased year by year,and they changed greatly from year to year.With the increase of year,the peak of nitrate nitrogen content moved downwards,but straw return can slow the downward movement of nitrate nitrogen.