Effects Of Integrated Soil-crop System Management Techniques On Soil Organic Carbon Sequestration And Stabilization Mechanisms In Phaeozems Of Northeastern

Soil organic carbon in farmland is the core of soil fertility and is an important factor to ensure crop production and food security.Therefore,current and future agricultural production is under multiple pressures to increase crop yields while reducing resource consumption and achieving environmental sustainability.Therefore,current and future agricultural production is under multiple pressures to further increase crop yields,reduce resource consumption and achieve environmental sustainability.Integrated soil-crop system management based on crop models and nutrient management design has been shown to help improve maize yields,but there is a lack of research on how to achieve increased maize yields while improving soil organic carbon sequestration and stability,and the impact of integrated soil-crop management techniques on soil microbial communities.Relying on the long-term positioning experimental platform for integrated soil-crop system management in Gongzhuling City,Jilin Province,four farm management systems（FP:Farmer Practice;IP:Improved Farmer Practice;HY:High Yield System;ISSM:Integrated Soil-Crop System Management）were explored,physical（soil aggregates）,chemical(¹³C-CPMAS NMR),microbial markers,and sequencing methods on the effects of soil organic carbon sequestration and stability mechanisms.The main results are as follows:（1）Integrated Soil-Crop System Management（ISSM）improves soil organic carbon sequestration and soil fertility.Based on a 12-year long-term locational trial,it was found that ISSM measures significantly increased soil organic carbon content and storage by 15%-87%and 11%-77%compared with other on-farm management measures.the relative rate of change of soil organic carbon and the average annual soil organic carbon sequestration rate were the fastest under ISSM measures,with a relative rate of change of soil organic carbon of 1.2 g C kg^-1 yr^-1 and an average annual soil organic carbon sequestration rate of 2.8 Mg C ha^-1 yr^-1.In addition,ISSM measures increased soil p H,decreased soil acidification,and increased a large number of available nutrients（available phosphorus,available potassium,and nitrate nitrogen）and exchange cation calcium,magnesium,and potassium contents,which in turn improved soil fertility.The results of the study showed that integrated soil-crop system management improved soil organic carbon content as well as soil fertility.Thus,ISSM measures achieved high crop yields and also improved soil organic carbon quality,and higher soil fertility and N fertilizer bias provided a good basis for high crop yields.（2）Integrated soil-crop system management increased soil agglomerate stability.Compared with FP practices,ISSM practices significantly increased the proportion of large aggregates,especially>2 mm aggregates,but decreased the proportion of 0.25-0.053 mm aggregates,indicating that ISSM practices had a positive effect on the formation of large macroaggregates.The responses of aggregate stability to different farm management measures were different;the mean weight diameter（MWD）and geometric mean diameter（GMD）were the largest under ISSM practices,the MWD and GMD were the smallest under FP practices.It shows that ISSM practices significantly improved the stability of aggregates.The ISSM practices increased the organic carbon content of the fractions in all particle size aggregates.The study suggests that integrated soil-crop system management enhances the physical stability of soil aggregates,which in turn promotes the accumulation of soil organic carbon.（3）Integrated soil-crop system management decreases the soil organic carbon chemical stability,but improved soil organic carbon availability.The study found that O-alkyl C（27.2%-29.5%）had the largest proportion of the four farm management practices,followed by Alkyl C（23.1%-26.2%）,Aryl C（16.3%-20.7%）and Carboxyl C（7.85%-9.17%）.Compared to the FP practices,ISSM practices increased 17.2%Methoxyl C and 8.1%O-alkyl C,indicating an increased proportion of unstable organic carbon fractions.The ISSM practices of Alkyl C/O-alkyl C,Hydrophobic C/Hydrophilic C,and Aromaticity did not improve compared with the FP practices,indicating that the soil organic carbon chemical stability was not improved,but the lower Alkyl C/O-alkyl C reflected that the ISSM practices delayed the soil organic carbon decomposition.In addition,the ISSM practice improved the Aliphatic C/Aromatic C ratio,indicating that the molecular structure of soil organic carbon tended to be simpler and easier to be decomposed and utilized by microorganisms,which improved the soil organic carbon quality.（4）Integrated soil-crop system management increased the diversity and abundance of bacterial and fungal communities.ISSM practices significantly increased the relative abundance of r-strategy microorganisms（Firmicutes,Bacteroidetes,Myxobacteria,Ascomycota,Mortierellomycota）.Soil p H,soil organic carbon,total nitrogen,available phosphorus,and available potassium were the main drivers of soil bacterial community diversity and composition.Soil p H,soil organic carbon,total nitrogen,available phosphorus,and exchangeable potassium ions are the main drivers of soil fungal diversity and composition.Integrated soil-crop system management practices promoted correlations between soil organic carbon functional groups and bacterial communities,particularly between the labile carbon groups O-alkyl C,Methoxyl C,and Firmicute,indicating that microorganisms have different substrate preferences and growth strategies thamediateste decomposition and accumulation in the soil.In this study,there was a significant positive correlation between Mortierellomycota and Methoxyl C.Glomeromycota showed a significant negative correlation with>2 mm aggregates and a significant positive correlation with 0.25-0.053 mm aggregates.Glomeromycota plays a crucial role in soil aggregation by"bonding"and promoting aggregate formation.（5）Integrated soil-crop system management increased the microbial necromass carbon content,thereby improving the soil organic carbon microbial stability.Microbial necromass carbon content increased 1.3-1.7 fold,bacterial necromass carbon increased 1.4-2.0fold,and fungal necromass carbon increased 1.3-1.7 fold under ISSM practices compared to the other three farmland management practices.The ratio of fungal necromass carbon content to bacterial necromass carbon content was reduced under ISSM practices compared to the other three on-farm management measures,indicating that bacterial necromass carbon content was a better determinant of soil organic carbon content increase than fungal necromass carbon content.Pearson correlation analysis showed that bacterial necromass carbon,fungal necromass carbon,microbial necromass soil organic carbon,total nitrogen,nitrate nitrogen（NO₃^--N）,microbial biomass carbon,and r/K strategy microbial ratios were significantly and positively correlated.Microbial necromass carbon is considered to be an important contributor to the persistent soil carbon pool,and ISSM measures significantly enhanced soil nutrient and carbon availability,promoting a shift in both microbial community life histories from the K to r strategy,a shift that led to a transient increase in microbial biomass carbon and thus increased soil organic carbon stock through the microbial necromass accumulation.In summary,integrated soil-crop system management achieves high crop yield and high efficiency while significantly improving soil organic carbon sequestration,increasing physical and biological stability of soil organic carbon,and improving soil microbial diversity and community composition,which will contribute to soil organic carbon sequestration and is important for the sustainable development of farmland.