Effects Of Conservation Agriculture On Soil Organic Carbon Fractions In Red Soil

Carbon cycling is an important basis for the material cycle in nature,and an important way for the material cycle and energy cycle of the ecosystem.Farmland soil carbon management is of great significance for sustainable crop production and maintenance of soil ecosystem functions.Dryland of red soil in southern China is an important resource for the development of agriculture and animal husbandry,However,the organic carbon content of red soil dryland is generally low,which is not conducive to maintaining soil health and sustainable agricultural development.numerous studies have explored its mechanisms,and the study of organic carbon fractions is helpful to reveal its internal mechanism.While few studies have focused on organic carbon fractions,especially the critical contribution of microbial residue carbon(MRC)to soil organic carbon.This study is based on a full-factorial experiment with three factors and two levers(without and with rice straw amended;without and with pig manure amended;conventional tillage and no-tillage),which has eight treatments to investigate the effects of conservation agriculture managements on soil organic components in subtropical red soil upland,and the contribution of organic carbon components to total soil organic carbon.The results are as follows:(1)No-tillage(NT)reduces soil organic carbon and its fractions.Compared with conventional tillage,NT reduces soil organic matter(SOC),particular organic matter(POM),mineral-associated organic carbon(MAOM),dissolved organic matter(DOC),microbial biomass carbon(MBC),and MRC by 11.48%,10.82%,18.12%,42.50%,39.02% and 11.40%respectively in 0～10 cm soil layer,in 10-20 cm soil layer,reduces POM,MAOM,DOC,MRC by 7.47%,13.16%,51.94% and 6.51% respectively.The effects of the amendment of pig manure on the organic carbon fractions is different in different soil layers.Compared without pig manure,the amendment of pig manure increases POM and DOC,and decrease MAOM,MBC and MRC in 0-10 cm soil layer;In 10～20 cm soil layer,increase DOC and MRC,decrease POM,MAOM and MBC.Compared without straw,the amendment of straw in the 0-10 cm soil layer increased SOC,POM,MAOM,DOC by 7.07%,9.65%,7.73% and53.69%,respectively;in 10-20 cm soil layer,POM and MAOM increased by 19.83%,11.96%,decreased DOC by 8.50%.(2)Tillage significantly affects the accumulation of amino sugar and microbial residue carbon.compared with conventional tillage(CT),the total amount of amino sugar increased by 21.06% and 22.31% in 0-10 cm soil layer and 10-20 cm soil layer under NT,respectively,which indicate that tillage promoted the accumulation of amino sugars in red soil farmland.NT and the addition of organic materials reduce the ratio of fungal glucosamine and muramic acid,indicating that NT and the addition of organic materials promotes the accumulation of bacterial residue carbon.The bacterial carbon and fungal carbon of the 0～10 cm soil layer are higher than those of the 10-20 cm soil layer,indicating that more microbial residue carbon accumulates in the 0-10 cm soil layer.Microbial residue carbon can account for 30.99% to58.12% of soil organic carbon.(3)Conservation agricultural managements increase the nutrient content in 0-10 cm soil layer,however,there is a trend to decrease the nutrient content in 10-20 cm soil layer.The amendment of pig manure significantly increased the soil p H,and the amendment of straw increased the soil p H to a certain extent.pig manure,NT decreased the total PLFA and the enzyme activities.Compared with CT,NT decreased the total PLFA by 10.52% and 20.30%in the 0-10 cm soil layer and the 10-20 cm soil layer,respectively.Regardless of the amendment of rice straw and pig manure,the soil base enzyme activity of CT tends to be higher than that of NT.(4)The random forest model shows that the aggregate size is a key factor affecting microbial residue carbon and soil organic carbon,Particulate organic carbon is a key factor affecting soil organic carbon.Linear regression analysis and structural equation models show that in the 0-10 cm soil layer,soil organic carbon is significantly positively correlated with POM and MAOM,and significantly negatively correlated with bacterial carbon.Organic materials amendment promotes DOC,tillage increases POM by increasing MBC and MRC,In 10～20 cm soil layer,soil organic carbon is significantly positively correlated with POM,DOM and fungal residue carbon.The amendment of pig manure increases MRC and bacterial residue carbon,tillage directly increases MAOM and indirectly increases MAOM by increasing fungal residue carbon.In general,organic materials amendment is beneficial to improve soil structure,increase soil p H,and increase soil nutrient content in the 0-10 cm soil layer.Tillage significantly affects soil microbiological properties,improves soil enzyme activity and microbial biomass,and promotes the accumulation of microbial biomass carbon and microbial residue carbon fractions,which in turn affects the accumulation of soil organic carbon in the soil,suggest that microorganisms play an key role in the turnover and accumulation of soil organic carbon.