Decomposition Process Of Wheat Straw And Effect Of The Process On Soil Nitrogen Cycle And Summer Maize Yield With Different Ways Of Returning Field

Straw is the most abundant and renewable biomass resource on the earth.Straw returning is an important measure to reduce straw burning,protect environment and improve water and soil environment.Straw returning can reduce the use of chemical fertilizer,improve the utilization rate of fertilizer and increase the yield of crops.A field experiment was conducted to investigate the decomposition and nutrient release characteristics of wheat straw under different returning fields,Meanwhile,the effects of wheat straw returning on soil nitrogen cycling,soil holding capacity,soil microbial biomass,nitrogen use efficiency,nitrogen residue rate and yield of maize were studied.The influence factors of straw decomposition and the effects of adding straw on soil microbial biomass nitrogen,microbial biomass carbon and soil respiration rate were investigated through soil culture experiment.The main results are as follows:1)The decomposing efficiencies of wheat straws in different treatments were from 37.75% to 68.34% after 85 d.The decomposition rate of wheat straw in straw-plowed treatment was significantly higher than that in straw-mulching treatment(P<0.05).During the whole process,the trend of its major component decomposing and its nutrient releasing were consistent with that of straw decomposition.The decomposition rates of straw and its major component and nutrients were much faster at the beginning stage than at the later stage and were higher in straw-plowed than in straw-mulching.In the major component degradation of straw,the hemicellulose degradation rate was highest and the lignin degradation rate was the lowest in all treatments.For the nutrient releasing,the potassium releasing rate was highest and the nitrogen releasing rate was lowest in all samples.The application of chemical fertilizer has no significant effect on the decomposition of wheat straw.2)The change of nitrate nitrogen and ammonium nitrogen content in the soil of straw mulching field showed a "M" trend.The change of nitrate nitrogen and ammonium nitrogen content in the soil of non-straw showed a "V" trend.The contentof nitrate nitrogen and ammonium nitrogen in the soil of the plough layer with single fertilizer treatment reached the maximum in the V10 stage and higher than the straw returning treatment.The content of nitrate nitrogen and ammonium nitrogen in the soil of the control treatment(CK)was higher than the straw returning treatment before the tasseling stage.Compared with no straw addition treatment,returning field straw has a stimulating effect on cellulose degrading bacteria and Azotobacter in the soil of the plough layer.The number of ammonifying bacteria,nitrifying bacteria and denitrifying bacteria in the topsoil was significantly higher than that in straw mulching(P<0.05)at V10 stage and the tassel stage in chemical fertilizer treatment.There was a vertical migration of nitrate nitrogen during the growth period of Maize by chemical fertilizer treatment,while straw returning had a certain interception effect on nitrate nitrogen.Nitrate accumulation in conventional fertilization + straw mulching for returning was obviously accumulated in 20-40 cm soil layer(P<0.05),which was beneficial to the absorption of nutrients by roots,increasing nitrogen utilization rate and reducing the risk of nitrogen pollution of water and soil.3)Compared with no fertilization,conventional fertilization,straw mulching+conventional fertilization,straw burial returning+ conventional fertilization of maize yield increased by 4.45%,16.49%,7.51% respectively and compared with the control treatment,the yield of corn with straw mulching treatment and straw burying treatment increased by 2.94%,1.24% respectively.the straw mulching + conventional fertilizer yield was significantly higher than that of conventional fertilizer production(P <0.05),the main reason is the increasing thousand-grain weight significantly.Compared with conventional fertilization,the utilization rate of nitrogen fertilizer of straw mulching returning + conventional fertilization,straw burial returning field +conventional fertilizer treatment increased by 14.19% and 10.22% respectively.The order of nitrogen uptake of single maize in each period was The straw mulching+conventional fertilization>The straw burial returning + conventional fertilization >The conventional fertilization >sThe traw mulching >The straw burial returning> The non-fertilization.The dry weight of corn stalk increased fastest during the V10 stage to the tasseling stage.After the tasseling stage,the nitrogen uptake ofmaize was mainly stored in the seed,and the dry weight increased slowly.4)The straw combined with nitrogen fertilizer(urea)promoted wheat straw decomposition(P<0.05),which increased by 22.71% in 30 days.In a certain range,high soil moisture content can accelerate decomposition rate of wheat straw.Compared with no straw treatment,straw microbial biomass,soil microbial biomass,soil respiration rate and the number of cellulose degrading bacteria increased by 52.77%,22.06%,56.11% and 190.97%,respectively.Therefore,combined application of nitrogen fertilizer,straw-decomposing inoculant and suitable soil moisture content is significant for returning straw to field.The research results provide theoretical basis for rational straw returning.