Effects Of Combined Application Of Organic And Inorganic Fertilizers On Carbon And Nitrogen Characteristics And Bacterial Community Structure Of Purple Soil

The reasonable combination of organic and inorganic fertilizers can make full use of the interaction of fertilizers,supplement the short of chemical fertilizers with the advantages of organic fertilizers,improve crop yields,improve soil structure and soil quality.However,the effects of combined application of organic and inorganic fertilizers on the content of purple soil carbon and nitrogen components,soil carbon sequestration mechanism and soil bacterial community structure under equal nitrogen conditions were not systematically studied.In order to study the effects of three different fertilization methods of only chemical fertilizer,organic-inorganic fertilizer application,and only organic fertilizer on carbon and nitrogen characteristics and bacterial community structure of purple soil.Four treatments were set in this study: CK: no fertilizer;T1: only chemical fertilizer,organic fertilizer N accounts for 0% of total N;T2: organic fertilizer-chemical fertilizer combination,organic fertilizer N accounts for 30% of total N;T3: only organic fertilizer,organic fertilizer N accounts for 100% of total N.The main findings were as follows:1.Fertilization increased the content of soil organic carbon and total nitrogen,dissolved organic carbon/nitrogen,soil microbial biomass carbon/nitrogen: organic fertilizer-chemical fertilizer combined treatment and only organic fertilizer treatment significantly increased the content of soil organic carbon,but each treatment's content of soil total nitrogen was not seen significant changes;the effects of only chemical fertilizer treatment and organic fertilizer-chemical fertilizer combined treatment on the content of dissolved organic carbon/nitrogen and microbial biomass carbon were comparable;only organic fertilizer treatment significantly increased the content of soil dissolved organic carbon,microbial biomass carbon /nitrogen.Only chemical fertilizer treatment significantly reduced soil carbon-nitrogen ratio.Fertilization significantly increased soil sucrase and urease activities: organic fertilizer-chemical fertilizer combined treatment significantly increased the above two soil enzyme activities.2.After the application of different fertilizers,the mineralization of soil organic carbon changed significantly,soil organic carbon mineralization rate gradually decreased with the incubation time and eventually flattens,which was in line with the logarithmic function.Application of organic fertilizers,especially organic fertilizer-chemical fertilizer combined treatment increased soil organic carbon accumulated mineralization,which was conducive to the release of soil nutrients;at the same time,decreased the proportion of soil organic carbon accumulated mineralization,which was conducive to improving soil carbon sequestration capacity.Fertilization didn't change the organic carbon skeleton structure of the soil.The compounds of soil organic matter were mainly alcohols/phenolic aliphatic compounds,carbohydrates,aromatic compounds and organic silicon compounds.Fertilization significantly changed the relative content of soil organic carbon functional groups.The structure of soil organic carbon was dominated by alkyl carbon.With the increase of the amount of organic fertilizer applied,the content of recalcitrant organic carbon components increased and the content of easily decomposable organic carbon components decreased.Organic fertilizer was more likely to improve soil organic carbon stability than chemical fertilizer.3.Fertilization affected the diversity of soil bacterial communities,only organic fertilizer treatment significantly increased the soil bacterial ? diversity index and the number of unique bacteria.The overall composition of soil bacteria was not much changed.The soil bacteria were mainly Proteobacteria and Actinobacteria,but the relative abundance of different bacteria changed.Only organic fertilizer treatment increased the relative abundances of Bacteroidetes,Acidobacteria,Planctomycetes and Firmicutes,while decreased the relative abundances of Actinobacteria and Gemmatimonadetes.Both PCA analysis and UPGMA cluster analysis showed that only organic fertilizer treatment had a greater effect on the soil bacterial community structure.RDA analysis showed that soil soluble organic carbon and microbial biomass carbon were the key factors driving the change of soil bacterial community structure.In summary: the typical purple soil in the Liangshan tobacco planting area of Sichuan was taken as the research object in this study.the effects of combined application of chemical fertilizers with decomposed rapeseed cake fertilizer on soil quality were systematically studied under conditions of equal nitrogen,which solved the problem of large input of chemical fertilizer and soil quality decline.It can provide a theoretical basis for local soil improvement and sustainable soil productivity improvement.