Effects Of Straw And Straw Ash Application On The Accumulation Of Soil Microbial Residual Carbon In Rice-rape Rotation System

Soil microbial residual carbon is an important component of soil stable organic carbon pool.The storage time of microbial residual carbon in soil is longer and it can promote the accumulation of soil organic matter.The application of straw and straw ash is the embodiment of straw resource utilization.Fertilization and crop rotation are important tillage measures.Therefore,it is of great significance to study the influence mechanism of the application of straw and straw ash on the formation and accumulation of soil microbial residual carbon in rice-oilseed rape rotation.In this research,the long-term rice tanker soil was used as the research object.Four treatments were selected: no fertilization(Control),chemical fertilization(NPK),straw and chemical fertilization(NPK+St),straw ash and chemical fertilization(NPK+FSt).From the perspective of bulk soil,organomineral complexes and aggregates,the effects of straw and straw ash application on soil microbial residual carbon accumulation and its internal mechanism were discussed.The microbial residual carbon was quantified by biomakers,the microbial community structure was determined by high-throughput sequencing,the chemical composition and stability of organic carbonization were analyzed by nuclear magnetic resonance spectroscopy,the organic and mineral complexes and aggregates of soil were obtained by physical grouping,and different forms of Fe/Al oxides and their bound organic carbon were chemically extracted.Pearson correlation analysis was used to jointly explore the influence mechanism of organic carbon,microbial community,organo-mineral complexes and aggregates on soil microbial residual carbon accumulation under the application of straw and straw ash in rice-rape rotation system,so as to provide theoretical reference for enhancing the increment of carbon sink in farmland ecosystem and improving the quality of cultivated land.The main research results are as follows:(1)Fertilization increased soil organic carbon content,straw and straw ash combined with fertilizer to promote soil organic carbon sequestration.Based on fertilizer application,the organic carbon content of whole soil,organo-mineral complexes and aggregates increased more in rice and oilseed rape seasons after straw and straw ash application.The proportion of resistant carbon pool increased significantly in rice season.Compared with straw and fertilizer application,the stability of soil organic matter was enhanced by increasing the proportion of soil inert carbon pool and the hydrophobicity index of organic carbon after the application of straw ash and fertilizer.(2)The application of straw combined with fertilizer increased the accumulation of microbial residual carbon in soil,but reduced its contribution to soil total organic carbon.The application of straw ash combined with fertilizer significantly reduced the content of microbial residual carbon and its contribution to soil total organic carbon.After fertilization,the contribution of soil microbial residual carbon to soil total organic carbon in rice and oilseed rape seasons was 38.2%-54.2%.The addition of straw ash reduced the quality of substrate available to microorganisms,thereby affecting microbial activity and reducing the formation and accumulation of microbial residual carbon.The increase of soil p H and bacterial Shannon index was not conducive to the accumulation of soil microbial residual carbon.(3)Straw and fertilizer application increased the content of microbial residual carbon in soil organo-mineral complexes and its contribution to soil total organic carbon in rice season,but the effect was opposite in oilseed rape season.Straw ash with fertilization increased the content of microbial residual carbon in soil complexes in rice and oilseed rape seasons and its contribution to soil total organic carbon in rice season.The contribution of microbial residual carbon to soil complexes organic carbon in rice and oilseed rape seasons was 38.2%-60.9%,and the contribution to soil total organic carbon was 28.5%-43.5%.Based on fertilization,the contribution of microbial residual carbon to soil total organic carbon was greater when straw ash application was applied than straw returning,which in rice season is larger than that in rape season.The accumulation of microbial residual carbon in the complexes was affected by the organic carbon content of the complexes,and the accumulation of fungal residual carbon in the complexes may be increased by binding with short-range ordered and colloidal chelated Fe/Al oxides.(4)After straw with fertilization was applied,the content of fungal residual carbon in soil aggregates increased and increased with the decrease of aggregate size,while the content of bacterial residual carbon decreased significantly in < 0.25 mm.The application of straw ash with chemical fertilizer significantly reduced the content of bacterial and fungal residual carbon in 0.053-0.25 mm.Straw ash affected the accumulation of microbial residual carbon in microaggregates mainly by affecting the contents of Fe/Al oxides and their binding organic carbon in crystalline and colloidal or chelated phases.The proportion of microbial residual carbon in soil total organic carbon decreased with the decrease of the particle size of soil aggregates.Based on chemical fertilization,the application of straw and straw ash reduced the contribution of microbial residual carbon to soil total organic carbon in soil aggregates in oilseed rape season.