Influence Mechanism Of Biochar On The Aggregates Stability Of Mollisols

The Mollisols region of Northeast China is in an irreplaceable position in the field of commercial grain in China,and it is also a big granary in China.Up to now,the soil water retention capacity has decreased,the organic matter has decreased,and the aggregate structure has been seriously degraded,which directly threatens the continuous increase of grain production.As a new type of soil conditioner,biochar is stable and difficult to decompose,and has broad prospects in soil degradation and remediation.In this experiment,two treatments were selected for the long-term positioning test of biochar returning to the field for fertilization established by the Hailun Experimental Station of the Chinese Academy of Sciences in 2011: NPK fertilizer(CK)and NPK combined with biochar(BC).3 repetitions.To study the effects of biochar on particle size distribution and stability of mollisols aggregates,organic matter content of aggregates and density components,organic matter structure of each component and bacterial community structure,and to deeply reveal the stability and mechanism of mollisol aggregates,aim is to provide theoretical basis for biochar amelioration of mollisols in northeast China.The main conclusions of this study are as follows:(1)Biochar increased the content of 0.5-1mm aggregates,promoted the agglomeration of <0.25 mm aggregates to larger aggregates,and improved the stability of aggregatesBiochar significantly increased the content of 0.5-1mm aggregates by 50.47%,and decreased the content of 0.053-0.25 mm and <0.053 mm aggregates by 24.43%and 19.95%,respectively,which promoted the agglomeration of micro-aggregates to large aggregates.The content of light fraction increased,which was beneficial to the storage of organic matter.Biochar significantly increased the average weight diameter,geometric mean diameter and aggregate content greater than 0.25 mm,decreased the fractal dimension and improved the stability of mollisol aggregates.Correlation analysis showed that biochar should be applied to improve the stability of mollisol aggregates.The content changes of 0.5～1mm,0.053～0.25 mm and <0.053 mm should be paid attention to.(2)Biochar increased soil organic matter,total nitrogen content and C/N,and enhanced aggregate stabilityBiochar increased the contents of organic matter,total nitrogen and C/N ratio in bulk soil,and significantly increased the contents of organic matter,total nitrogen and C/N ratio of soil aggregates with <1mm grain size.Meanwhile,it increased the contribution rate of soil aggregates with 0.5-1 mm grain size to total organic carbon and total nitrogen,and decreased the contribution rate of soil aggregates with<0.25 mm grain size.Stepwise regression analysis showed that biochar promoted the transfer of carbon and nitrogen nutrients to large aggregates,which was of great significance for improving soil carbon sequestration and the redistribution of organic carbon and nitrogen in large aggregates.Biochar significantly increased the organic matter content,total nitrogen content and C/N ratio of the light fraction,and promoted the C/N cycling of the component.Biochar indirectly promoted the stability of soil aggregates by increasing soil carbon and nitrogen content and cation exchange capacity.(3)Biochar made the organic matter structure of bulk soil and macro-aggregates tend to be aliphatic,and improved stability of micro-aggregatesBiochar increased the relative abundance of aliphatic-CH,alcohol-phenol-OH and polysaccharide C-O,but decreased the aromatic C=C and carbonyl C=O,and increased the ratios of-CH/C=C and-CH/C=O.The relative abundance of aliphatic-CH and alcohol-phenol-OH increased,while the aromatic C=C and carbonyl C=O decreased in >2mm aggregate.The change was opposite in <0.25 mm grain size.According to principal component analysis,biochar led to aliphatic organic matter structure in bulk soil and large aggregates,and improved stability of organic matter in small aggregates.In the density component,biochar enhanced the activity of organic matter of light fraction,which was beneficial to accelerate the turnover and regeneration of soil organic matter.(4)Biochar increased the relative abundance of actinomycetes and spore monomycetes,and decreased the relative abundance of β and γ-proteobacteria,which promoted the stability of aggregatesBiochar changed bacterial community diversity and richness at phylum,class and genus levels.The relative abundance of actinomycetes and spore monomycetes increased by 57.61% and 20.93% respectively,which promoted the formation and stability of aggregates.Biochar enhanced the activity of Nitrospirae and increased nitrogen availability in soil.The relative abundance of β and γ-proteobacteria in soil decreased by 48.59% and 182.21%,respectively,which played an important role in improving soil nitrogen fixation ability.Biochar significantly increased the relative abundance of actinomycetes and promoted actinomycetes to decompose organic matter during the carbon cycle.The long-term effects of biochar on soil bacterial community structure were indirectly driven by changes in soil p H,organic carbon,total nitrogen and C/N.In conclusion,biochar improves aggregates stability by affecting soil physical and chemical properties and microbial community abundance,and comprehensively reveals the mechanism of biochar’s influence on aggregate stability of mollisol.The enhancement of soil aggregate stability contributed to the improvement of soil overall function and ecological restoration process.The application of biochar is an effective measure for soil improvement in Northeast China,which can be popularized in the restoration of traditional farmland.