Long-term Tillage Impacts On Soil Aggregate Organic Carbon And Microbial Community Diversity

Soil aggregate stability and microbial diversity play important roles in soil organic carbonstabilization in different tillage systems. We studied the influence of various tillage systems on soilorganic carbon (SOC) and also on microbial diversity in different sized soil aggregates after15years ofcontinuous wheat-fallow cropping system in the agriculture department dryland agricultureexperimental station in Henan province. Tillage treatments included reduced tillage (RT), no-tillage(NT), sub-soiling with mulch(SM), wheat-peanut two crops (TC), and conventional tillage (CT). Theaggregates size distributions were examined by dry and wet sieving method, and soil microbial(bacterial, archaeal and fungal) diversity were investigated by using the techniques of denaturinggradient gel electrophoresis (PCR-DGGE) analysis. The article aimed at offering basis for the theory ofsoil carbon stabilization and establishing best tillage mehod for a loess soil located Henan province. Themain results are summarized as follows:1. SOC content in the0-20cm soil layer increased in NT, SM and TC after15years treatment.SOC content in the0-10cm soil layer in NT, SM and TC was increased by11.5%,5.5%and6.9%respectively. In the10-20cm soil layer, the acceleration was decreased. In the20-30cm soil layer, SOCcontent in CT was higher than NT and SM.2. SM and NT could raise the yield of winter wheat. NT didn’t raise the yield in the early period,but gradually raised the yield with the increase of experiment year. Annual average yield of NT was3.1%larger than CT. SM raised the yield with application going on, and its annual average yield was6.5%larger than CT.3. The contents of＞250μm dry and water-stable aggregates were increased in NT and SM at the0-20cm soil depth. In the0-10cm soil layer, RT had the highest content of＞2000μm dry aggregateand the mean weight diameter (MWD) of dry aggregate. NT and SM increased the contents of1000-2000μm and250-1000μm dry aggregates. The macro-aggregate content (R0.25) of dry aggregatewas increased significantly in RT, NT, and SM. In the10-40cm soil layer, NT and SM increased thecontents of＞2000μm,1000-2000μm and250-1000μm dry aggregates, MWD and R0.25of dryaggregate. The contens＞53μm water-stable aggregates, MWD and R0.25of water-stable aggregateunder NT, SM and TC were obvious higher than CT at the0-20cm depth, but didn’t have significantlydifference at the20-30cm depth. SM had the lowest MWD and R0.25of water-stable aggregates at the30-40cm depth.4. The contents of SOC in＞250μm dry and water-stable aggregates were increased in NT, SMand TC at the0-20cm soil depth. NT, SM and TC increased the contents of SOC in all sizes dryaggregates in the0-20cm soil layer. In20-30cm soil layer, the contents of SOC in all sizes dryaggregates in CT were higher than NT. In30-40cm soil layer, SM had the lowest contents of SOC in allsizes dry aggregates. SOC contents in＞250μm water-stable aggregates increased in NT, SM and TCat the0-20cm soil depth. In20-40cm soil layer, SOC contents of＞250μm water-stable aggregates increased in CT inversely.5. The content of active SOC was increased in NT, SM and TC. Compared with CT, The content ofdissolved organic carbon (DOC) in NT, SM and TC was increased by22.7%,38.1%and24.7%respectively, microbial biomass carbon (MBC) was increased by32.5%,52.1%and43.7%respectively,light fraction organic carbon (LFOC) was increased by44.7%,45.0%and61.7%respectively, coarseparticulate organic carbon (coarse POC) was increased by17.7%,21.2%and21.8%respectively, andfine particulate organic carbon (fine POC) was increased by27.6%,29.8%and24.9%respectively. Thecontents of iccorporated organic carbon (IOC) of five treatments were no difference. NT, SM and TCsignificantly increased the contents of DOC in＞2000μm,1000-2000μm and＜250μm aggregates,and the contents of MBC in1000-2000μm,250-1000μm and＜250μm aggregates. The content ofLFOC in＞250μm aggregate were obvious higher than in＜250μm aggregate, and the contents ofLFOC in all sizes aggregates were increased in NT, SM and TC, The contents of coarse POC and finePOC in all sizes aggregates increased in NT, SM and TC, too. IOC contents in all sizes aggregatesincreased in CT inversely.6. NT, SM and TC caused the increasing in soil bacterial, archaeal and fungal communitydiversities. With NT, SM and TC, the bacterial Shannon-wiener index was increased by0.3%,0.3%, and0.6%, respectively, the archaeal Shannon-wiener index was increased by20.2%,40.5%, and49.1%, andfungal Shannon-wiener index was increased by23.7%,19.5%, and25.8%, as compared with CT.7. NT, SM and TC caused the increasing at different extent in bacterial, archaeal and fungalcommunity diversities in different soil aggregates. Both Shannon-wiener index and richness of bacterialwere higher in1000-2000μm and250-1000μm aggregates, and Shannon-wiener index and richness ofarchaeal were higher in＞250μm aggregates. while the fungal Shannon-wiener index was not obviouschanged along with aggregate variation. NT, SM and TC also caused the increasing at different extent inbacterial, archaeal and fungal community diversities in all sizes aggregates.In conclusion, conservation tillage, including NT and SM, and crop rotation, including TC,significantly improved the distribution and stability of surface soil water-stable aggregates, along withaggregate active SOC content and bacterial, archaeal and fungal community diversity, it suggested thatit is a more sustainable system for the loess hilly region of China.