Straw Microbial Inoculant Mediates Temporal Dynamics of Soil Erodibility via Regulating Soil Structure Through Distinct Pathways

ABSTRACT Straw microbial inoculants are supposed to facilitate straw decomposition, increase soil organic matter content, and enhance soil structure, thereby affecting soil erodibility. Nevertheless, the response of soil erodibility variations to their application as well as the underlying mechanisms remains poorly understood. To address this gap, a comprehensive soil erodibility index (CSEI) derived from eight soil erodibility indicators of soil cohesion (Coh), penetration resistance (PR), mean number of drop impacts (MND), mean weight diameter (MWD), saturated hydraulic conductivity ( K s), slaking rate (SR), soil erodibility factor K ( K ), and structural stability index was applied to reflect soil erodibility. Soil erodibility indicators were measured under five straw microbial inoculants application rates (SMIAR) of 0 (as control, CK), 1, 2, 3, and 4 kg hm −2 monthly during the whole corn growing season, then CSEI as well as ∆CSEI (relative changes in CSEI compared to control) were calculated. The results showed that CSEI exhibited a significant decreasing trend, whereas ∆CSEI displayed a relatively stable stage under SMIAR of 1 and 2 kg hm −2 , and exhibited an overall decreasing trend under SMIAR of 3 and 4 kg hm −2 during the whole corn growing season. And CSEI and ∆CSEI decreased significantly as SMIAR increased. Compared to CK, CSEI decreased by 11%, 22%, 37%, and 47% under SMIAR of 1, 2, 3, and 4 kg hm −2 , respectively. However, no significant differences in CSEI were detected between SMIAR of 3 and 4 kg hm −2 , indicating that 3 kg hm −2 could be the optimal SMIAR for regions with similar conditions. Despite both the temporal variation in CSEI and ∆CSEI being primarily governed by the changes in soil structure driven by straw decomposition, their regulation pathways differed completely. Changes in soil structure driven by the month regulated the temporal variation in CSEI. In contrast, changes in soil structure induced by microbial inoculants controlled the temporal variation in ∆CSEI. These findings provided a deeper understanding of how straw microbial inoculants regulate soil erodibility and offer practical recommendations for optimizing SMIAR in purple soil sloping farmland.