Soil microbial decomposition of agricultural wastes shapes soil aggregation enhancing organic carbon content in the soils under different land-uses in southwest Bangladesh

Soil aggregates are important for aeration, microbial activity, root growth, and infiltration. Soil aggregation can vary depending on microbial activity, soil organic carbon (SOC), and soil management practices. However, the underlying drivers and mechanism of aggregation under different land-uses in southwest Bangladesh remain largely unknown. The objective of current study was to explore the underlying mechanism of aggregation in the soils of southwestern Bangladesh. In current study, soil samples were collected from three widely practiced rice-based land-uses (fallow–rice–fallow, fallow–rice–watermelon, and shrimp–rice–fallow) across the Khulna district of southwest Bangladesh. Results exhibited that the aggregate stability indicated by mean weight diameter (MWD) in fallow-rice-fallow and fallow-rice-watermelon were significantly greater than shrimp-rice-fallow land-use (P < 0.05). Microbial activity in fallow-rice-fallow land-use was 3 times higher than shrimp-rice-fallow land-use (P < 0.05). SOC was also higher in the fallow-rice-fallow and fallow-rice-watermelon land-uses than shrimp-rice-fallow land-use. Scanning electron microscopy and Fourier transform infrared spectroscopy results indicated aggregated morphological features and greater polysaccharides intensity in fallow–rice–fallow and fallow–rice–watermelon land-uses, respectively. A positive relationship was found between microbial biomass carbon (MBC) and MWD (r = 0.56; P < 0.01), and between SOC and MWD (r = 0.38; P < 0.05), indicating the dominant role of soil microbes in aggregation and the enhancement of SOC. Principal component analysis results also support the dominant role of MBC and SOC in aggregation and identified two distinct land-uses based on the soil properties. The study results demonstrate that microbial activity plays a key role in aggregation, enhancing the decomposition of agricultural waste and increasing SOC under investigated land-uses of southwest Bangladesh.