| China is rich in straw resources,and straw returning is an important way to realize fertilizer utilization.However,the long-term return of straw to the field results in the accumulation of a large number of undecomposed organic residues in the soil,which easily leads to the imbalance of C/N in farmland,the above factors will affect crop growth.Through reasonable tillage and farmland fertilization management measures,the depth,hydrothermal conditions and microbial conditions after straw returning can be changed,and the C/N ratio of farmland soil can be balanced,thus promoting the decomposition of straw and the sustainable development of farmland ecosystem.Based on the above,a two-year field experiment was carried out in this study.Different tillage methods（CPT,ZT and PT）and different nitrogen application rates(N1:180 kg N·hm-2,N2:240 kg N·hm-2,N3:300 kg N·hm-2)were set up,and the nylon net bag method was used to study the returning to the field As well as the dynamic response of soil physical and chemical properties and microbial abundance,in order to find the best combination scheme of tillage methods and nitrogen fertilizer application rate,and provide scientific basis and technical support for achieving the goal of improving soil fertility and stabilizing crops.The main research results are as follows:（1）From the farming point of view,compared with PT,conservation tillage CPT and ZT can increase the content of soil organic carbon,water content,nitrate nitrogen and ammonium nitrogen,while the content under N2 is significantly higher than that under N1and N3.From the interaction between tillage and nitrogen fertilizer,ZT-N2 can significantly improve the effect of fertilizing farmland compared with other tillage methods and nitrogen fertilizer combinations.Compared with PT,CPT and ZT significantly increased soil microbial biomass nitrogen,and increased application of nitrogen fertilizer could also increase soil microbial biomass nitrogen under the same tillage treatment.Tillage and nitrogen fertilizer have significant interactive effects on microbial gene abundance.CPT and ZT can significantly increase the abundance of cbh I,lac gene and fungi,while PT can increase the abundance of bacteria.The abundance of cbh I,lac gene and fungi performed well under N2 condition,and the abundance of bacteria increased with the increase of nitrogen fertilizer amount under the same tillage treatment.On the whole,ZT-N2 treatment is a suitable farmland management measure under the experimental conditions.（2）Under different treatments,the final decomposition rate of wheat straw reached 53%.At this time,the whole structure of wheat straw was seriously damaged,and the whole structure was broken in segments.The two-year decomposition process showed a gradual change trend of fast decomposition in the early stage and slow decomposition in the later stage,with the highest decomposition rate reaching 0.24 g·d-1.Generally speaking,ZT has a significant impact on promoting straw decomposition compared with CPT and PT.Under ZT treatment,nitrogen application rates under N1 and N2 can significantly increase the decomposition rate of wheat straw.Therefore,ZT-N1 and ZT-N2 treatments can decompose straw faster under the experimental conditions.Meanwhile,soil nitrate nitrogen and ammonium nitrogen have a significant positive correlation with straw decomposition rate,while organic carbon has a significant negative correlation with straw decomposition rate.（3）Tillage,nitrogen fertilizer and the interaction between tillage and nitrogen fertilizer have significant effects on grain yield.Under ZT-N2 treatment,summer maize has the highest yield of 7502.5 kg·hm-2.The changes of crop yield components under different treatments are different:ZT can increase the number of grains per spike and grain yield of summer maize,and CPT can significantly increase the 100-grain weight of summer maize;N2 treatment can increase the number of grains per spike and grain yield of summer maize,while N1 treatment can increase the 100-grain weight.According to comprehensive analysis,the farmland management measures of returning straw without tillage combined with applying nitrogen fertilizer of 240 kg N·hm-2 can significantly improve soil physical and chemical properties,increase soil microbial abundance,promote straw decomposition and transformation,and promote the yield formation of summer maize.It is a more obvious way of returning straw to the field for soil fertility and stable crop yield under the experimental conditions. |
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