Effect Of Biochar And Organic Materials On DOM And Anaerobic Iron Reduction In Paddy Soils

Biochar is a substance produced by the cracking of biomass under high temperature and anoxic conditions.In recent years,it has achieved good results in improving soil,increasing crop yield,and repairing heavy metals in soil.The application of biochar to the soil can affect the microbial community structure in the soil,promote the respiration of the paddy soil,and can significantly increase the microbial reduction rate of iron oxide.In the preparation process of biochar,a large amount of pyroligneous liquor would be produced,it can change the pH and conductivity of the soil after applying to the soil,which may promote the microbial iron reduction process in the soil.Humic acid is the most common natural organic substance in terrestrial and aquatic environments and can play an important role in the iron reduction process as an electron shuttle.It has been pointed out that dissolved organic carbon is closely related to iron reduction process.Therefore,by exploring the changes in the structure and composition of dissolved organic matter?DOM?in the soil where biochar and organic materials are applied,the mechanism of the influence on the iron reduction process in soil can be better understood.In this study,the anaerobic mud culture test and rice potting planting experiment were carried out by adding biochar,wood vinegar,humic acid and biochar were combined with organic materials to analyze the contents of dissolved organic carbon?DOC?,DOM composition,iron reduction characteristics,rice biomass and chlorophyll content in each treatment.The main conclusions were as follows:?1?Biochar and pyroligneous liquor reduced the root-shoot ratio and biomass of rice,and increased the chlorophyll content,which showed a weak inhibitory effect on rice growth.The humic acid was different due to the different soils in rice planting.The addition of humic acid to the Ankang paddy soil increased the dry weight of the aboveground and underground parts of the rice and decreased the chlorophyll content,while the addition of humic acid to the Hanzhong rice soil increased the dry weight of the aboveground and underground parts of the rice,and the chlorophyll content first increased and then decreased.?2?Biochar could promote microbial iron reduction in paddy soil and increase DOC content and SUVA₂₅₄ in paddy soil.The main component and relative amounts of different soils identified by three-dimensional fluorescence spectrum characteristics were different.The addition of biochar not only increased the soil fulvic acid in Hunan acid paddy soil,but also changed the relative content of each component.The effect of biochar on the component and content of the near neutral Tianjin paddy soil and the strongly alkaline Jilin paddy soil was small,especially in TJ paddy soil.The correlation analysis revealed that the addition of biochar can affect the nitrate reduction,iron reduction and methanogenesis in anaerobic paddy soil by adjusting the SUVA₂₅₄,component of DOM and the pH of the system.?3?The effect of pyroligneous liquor on the anaerobic iron reduction of paddy soil was obvious,and it also had certain effect on regulating the initial pH value of soil.The addition of pyroligneous liquor increased the DOC content of paddy soil and increased the absorption characteristic value of DOM.The types and relative contents of DOM dominant components in different types of paddy soils were different.The addition of pyroligneous liquor had a greater influence on the relative content of DOM in rice,but had no significant effect on the components of DOM.Correlation analysis showed that DOC content,soil fulvic acid and tyrosine-like changes all affected the iron reduction ability of HN paddy soil.The iron reduction ability of TJ paddy soil was affected by DOC content,SUVA₂₅₄ and high molecular weight humic acid relative content.And the enhancement of iron reduction ability in JL paddy soil was greatly affected by SUVA₂₅₄.?4?Humic acid could regulate soil iron reduction ability,increase iron reduction potential and reduction rate,and has obvious effect on pH regulation in strong alkaline paddy soil.The addition of humic acid increased the DOC content and aromatic matter in paddy soil,which changed the relative content of DOM components and had no significant effect on the dominant components of DOM.Components included high molecular weight humic acid?UVC?,low molecular weight humic acid?UVA?,soil fulvic acid,tyrosine-like and Microbial humic acid.Correlation analysis showed that the microbial iron reduction ability and pH value of paddy soil were controlled by DOC content,SUVA₂₅₄ and DOM.?5?The combination of biochar and organic materials could promote the reduction process of iron oxide in paddy soil,and generally increase the DOC content and UV spectral characteristic value(SUVA₂₅₄)in soil,and change the DOM component category.The soil fulvic acid was increased in HN paddy soil,the low molecular weight humic acid was added in the TJ paddy soil.However,the dominant component categories of DOM in JL paddy soil didn't change,and the relative content of each component changed significantly.Correlation analysis showed that the redox process was greatly affected by DOC content,SUVA₂₅₄ and pH.The addition of biochar and organic materials affected the redox process by affecting DOC content,SUVA₂₅₄ and pH in soil.