Effects Of Straw Returning And Water And Nitrogen Regulation On Soil Nutrients、Enzyme Activities And Microbial Populations

China is at the forefront of straw production in the world,its average utilization rate is 32%,and 35%of crop straw is disposed of by burning in the production process,which not only leads to air pollution and waste of resources,but also affects the coordinated development of agriculture and ecological environment.Nitrogen application and irrigation measures have been considered as important measures to improve soil nutrients and crop yield in agricultural production.In order to implement the concept of green agricultural development and to establish the concept of conservation and recycling of resources,this paper carried out a research experiment on straw returning and water and nitrogen regulation by means of outdoor plots and indoor culture.Under the full amount of straw returning to the field,five treatments were set up in the plot experiment:Irrigation with regular nitrogen application(Long-lasting compound fertilizer 750kg·hm^-2(Nitrogen200kg·hm^-2,Phosphorus 90kg·hm^-2,Kalium 90kg·hm^-2)),No irrigation with regular nitrogen application,Irrigation with reduced nitrogen application（30%reduction from regular fertilizer application）,No irrigation with reduced nitrogen application,and CK（No irrigation and No nitrogen application）.Irrigation was applied by shallow buried drip irrigation at 80%of the field water holding capacity.Seven treatments were set up in the indoor culture experiment:W₁N₁(Soil moisture60%～70%,Nitrogen application 140kg·hm^-2),W₂N₁(Soil moisture 70%～90%,Nitrogen application140kg·hm^-2),W₃N₁(Soil moisture>90%,Nitrogen application 140kg·hm^-2),W₁N₂(Soil moisture60%～70%,Nitrogen application 200kg·hm^-2),W₂N₂(Soil moisture 70%～90%,Nitrogen application200kg·hm^-2),W₃N₂(Soil moisture>90%,Nitrogen application 200kg·hm^-2),and CK（Soil moisture70%～90%,No nitrogen application）.The effects of total straw returning and water and nitrogen regulation on soil nutrient content,soil microbial population and enzyme activity,and maize yield were investigated comprehensively to provide a theoretical basis for the realization of efficient and sustainable utilization of straw resources,scientific water and nitrogen management methods,and green agriculture.The results of the experimental study are as follows.（1）The effect of water and nitrogen regulation on straw decomposition rate under full amount of straw returning to the field was significant.By the 90th day,more than 35%of straw in each treatment had decomposed.It showed a trend of rapid decomposition in the early stage and slower decomposition in the later stage,and the degree of decomposition was higher with nitrogen application than without nitrogen application.（2）Straw returning and water and nitrogen regulation also increased soil nutrient content,soil enzyme activity,and soil microbial population,which also contributed to maize yield components and maize yield.At soil moisture content 70%～90%,the total soil nitrogen content with nitrogen application of 200kg·hm^-2 was greater than that with nitrogen application of 140kg·hm^-2.At the same soil moisture content,the total phosphorus content with nitrogen application of 200kg·hm^-2was greater than that of 140kg·hm^-2 by as much as 0.05%,indicating that suitable soil moisture content and nitrogen application could effectively increase the total phosphorus content of the soil and enhance the soil environment.At the same soil moisture content,the effective phosphorus content with nitrogen application of 200kg·hm^-2 was greater than of 140kg·hm^-2.The greater the soil moisture content,the higher the effective phosphorus content in the soil at the same nitrogen application rate.The organic carbon content increased first and then decreased,and the higher the nitrogen application,the higher the organic carbon content at the same soil moisture content.Soil sucrase,urease and cellulase activities showed a trend of increasing and then decreasing,and the sucrase activity of W₂N₁ was the highest at 19.26mg·g^-1·d^-1 on the 30th day of incubation,and the soil sucrase activity increased because the application of nitrogen fertilizer as the carbon and nitrogen elements cycled faster and the soil quality improved significantly.Soil urease activity was highest at soil moisture 70%～90%under the same nitrogen application rate.Soil cellulase activity was highest at nitrogen application 140kg·hm^-2 and soil moisture content>90%.The number of soil bacteria tended to increase and then decrease during the incubation time,and the highest number of soil bacteria was found at the soil moisture 70%～90%under the same nitrogen application.The higher the amount of applied nitrogen under the same soil moisture content,the higher the number of soil bacteria.The number of soil fungi showed a gradually increasing trend,and the highest number of soil fungi was found at the soil moisture 70%～90%and nitrogen application 200kg·hm^-2.Straw returning and water and nitrogen regulation were particularly important for maize growth,where the best growth and highest yield of 12,500kg·hm^-2 was achieved in the irrigated conventional nitrogen application treatment,which increased 38.9%compared with CK.（3）In a way,The straw decomposition rate could reflect the changing pattern of soil nutrients,and the straw decomposition rate was highly significantly and positively correlated with soil total nitrogen,organic carbon content,the number of soil bacterial and the number of soil fungi.Soil total nitrogen content was highly significantly and positively correlated with soil sucrase,urease activity and soil bacterial population.The indicators interacted with each other and had an intrinsic relationship.