The Effects Of Conservation Tillage And Straw Residue Incorporation On Soil Nutrients And Bacterial Communities In Lime Concretion Black Soil

Due to the high intensity utilization of the lime concretion black soil,the soil fertility is declining,which restricts the sustainable development of agricultural production.In this study,a variety of straw residue incorporation and conservation tillage managements were combined to improve soil fertility and investigate the changes of soil bacterial community.Soil samples were taken from the bulk and rhizosphere soil at the bell stage of maize and heading stage of wheat with six treatments: control(CK,conventional tillage without straw retention),conventional tillage combined with straw retention(SR),reduced tillage combined with straw retention(RSR)and no tillage combined with straw retention(NSR),conventional tillage with born straw return(BSR)and conventional tillage with incomplete born straw return(ICR).The bacterial 16 S rDNA was amplified from each soil sample and sequenced using high-throughput sequencing on Illumina MiSeq platforms.The main results showed as bellow:(1)straw residue incorporation and conservation tillage had no significantly influence of soil pH,conservation tillage(RSR and NSR)affected soil total nitrogen(TN),soil organic matter(SOM),soil available N and available K.ICR significantly increased the contents of TN,SOM,available N and available K.BSR significantly decreased the available N in bulk soil,and TN as well as SOM in rhizosphere soil.(2)The average yield of maize was increased by the conservation tillage and straw residue incorporation,which was increased by 2.15%~10.69%.ICR had the highest increasing effect on maize yield.Only ICR increased the average yield of wheat compared to CK,whereas other four treatments cannot enhance the yield of wheat.(3)In the maize bell stage and wheat heading stage,conservation tillage(RSR and NSR)had a higher OUTs than other treatments both in bulk and rhizosphere soil,whereas BSR had a the lowest OTUs.In the maize bell stage,conservation tillage(RSR and NSR)and ICR increased the richness of bacteria,whereas SR and BSR had no significantly influence of bacterial richness.In the wheat heading stage,SR and ICR both can enhance the bacterial richness,and the richness also had variations between bulk and rhizosphere soil.In the maize bell stage,straw residue incorporation and conservation tillage cannot enhance the diversity of bacteria,but significantly increased the bacterial predominance in rhizosphere soil,in contrast,had no significantly influence of bulk soil.In the wheat heading stage,straw residue incorporation and conservation tillage cannot significantly increased the bacterial diversity in bulk soils,however,ICR significantly increased the bacterial diversity in rhizosphere base on Shannon index.Compared to BSR,ICR increased the Shannon index by 19.75% in rhizosphere soil.Bacterial predominance was significantly influence by straw residue incorporation and conservation tillage,as well as influence by the different soil environment between bulk and rhizosphere.(4)A linear relationship was observed between the relative abundance of some phyla and the contents of soil nutrients.In the maize bell stage,the relative abundance of Acidobacteria was positively correlated with soil pH,whereas,was negatively correlated with soil available N;the relative abundance of Actinobacteria was negatively correlated with soil pH and positively correlated with soil available P.The relative abundance of Bacteroidetes and Candidatus were both positively correlated with soil available P.The relative abundance of Chlamydiae was positively correlated with soil pH and negatively correlated with soil SOM and available P.The relative abundance of Cyanobacteria was negatively correlated with soil available K.In the wheat heading stage,the relative abundance of Acidobacteria,Bacteroidetes,Planctomycetes and Candidate were negatively correlated with soil available K.In addition,the relative abundance of Chlamydiae was positively correlated with soil available N,TN and SOM.The relative abundance of Chloroflexi was positively correlated with soil available N and was positively correlated with soil available K.The relative abundance of Gemmatimonadetes was positively correlated with soil TN and SOM.The relative abundance of Verrucomicrobia and Candidate was negatively correlated with soil available P and available N,respectively.(5)To display the similarity and variations in the soil bacterial compositions of each treatments and their relative abundance variations more directly,clustering results for the top 50 genera with the most OTUs were displayed on a heatmap diagram.In the maize bell stage,based on the similarities between the composition,all treatments were divided into two groups,one for the conservation tillage with straw return(RSR and NSR)both in bulk and rhizosphere soil samples,and another for CK and conventional tillage(SR,BSR and ICR)which can be further divided into two groups based on bulk and rhizosphere soils.In the wheat heading stage,all treatments were generally clustered into four groups,SR and RSR in rhizosphere soils were clustered into one group,ICR in bulk soil,CK,NSR and ICR in rhizosphere soil were clustered into one group,SR,RSR and NSR in bulk soil were clustered into one group,CK in bulk soil and BSR both in bulk and rhizosphere soil were clustered into one group.Both in the maize bell stage and wheat heading stage,bacterial communities of RSR and NSR in bulk soil were much similar.The compositions of bacteria in the six treatments largely varied in both the dominant phylum and the relative abundance of each phylum.In addition,the dominant phylum and their relative abundance also varied between bulk and rhizosphere soil.Conservation tillage and ICR significantly affected the composition and the structure of bacteria.The changes of richness and diversity in rhizosphere soil were much higher than in bulk soil under the conditions of conservation tillage and straw residue incorporation.