Objective This study was to provide a scientific basis for rantional utilization of organic materials and improving soil structure by investigating the effects of combined application of chemical fertilizers with different organic materials on soil water-stable aggregates and organic carbon sequestration.

Method A field experiment was conducted with maize as the tested crop, including five treatments: sole chemical fertilizer (CK), chemical fertilizer with sheep manure (AF), chemical fertilizer with cassava residues (PF), chemical fertilizer with woody peat (MF), and chemical fertilizer with monosodium glutamate waste pulp (IF). The soil organic carbon fractions and water-stable aggregate contents were measured under different treatments.

Result Compared to CK, the soil total organic carbon (TOC) content in soils treated with various organic materials increased by 7.93% to 24.67%, and the contents of dissolved organic carbon (DOC), readily oxidized organic carbon (ROC), and microbial biomass carbon (MBC) increased as well. Among them, the IF treatment had the highest TOC and ROC contents but the lowest MBC content, while the AF treatment had the highest DOC content. The MF treatment had the highest MBC content but the lowest TOC, DOC, and ROC contents. The allocation ratios of active carbon fractions in total organic carbon differed among the organic material treatments. Only the AF treatment showed an increase in DOC/TOC compared to CK, but all organic material treatments led to an increase in ROC/TOC and MBC/TOC. Application of organic materials significantly increased the contents of soil water-stable aggregates in the 1-2 mm and 0.5-1 mm size fractions, promoting the formation of larger aggregates (>0.25 mm) as well. The proportion of soil water-stable aggregates within the 2-5 mm size fraction was highest across treatments. After applying organic materials, the content of large water-stable aggregates increased by 17.64% to 30.48%, and the mean weight diameter (MWD) of the water-stable aggregates followed the trend of AF > PF > IF > MF > CK. The correlation analysis revealed a significant positive relationship between DOC and the content of soil water-stable aggregates in the macro-aggregate fraction (>0.25 mm), as well as the mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates. This finding suggested that higher level of DOC contributed to enhance stability of soil aggregates.

Conclusion Overall, the application of MSG waste pulp exhibited the greatest effectiveness in enhancing soil organic carbon content, while the application of sheep manure resulted in the highest stability of soil water-stable aggregates.