Soil structural integrity as a driver of soil organic carbon persistence in sandy loam tropical Oxisols

This study evaluated the effects of forest conversion to pasture and cropland on soil structural condition and soil organic carbon (SOC) stocks in sandy loam tropical Oxisols. An integrated framework combining physical soil attributes (bulk density, porosity, and aggregate stability), soil degradation (SDI) and structural resilience (SRI) indices, and principal component analysis was applied. A consistent land-use gradient (forest > pasture > cropland) was observed, with forest soils showing higher structural quality and SOC stocks. Pasture exhibited intermediate conditions, particularly in subsurface layers (10–20 cm), while cropland showed reduced SOC stocks, increased bulk density, and lower aggregate stability. PCA confirmed clear separation among land uses, with soil compaction and aggregate stability driving differentiation, especially at 10–20 cm depth. SOC stocks were positively associated with macroporosity and aggregate stability and negatively associated with bulk density and microporosity. Overall, results indicate that soil structural condition is closely linked to SOC persistence in sandy tropical soils. The integrated use of structural indices and multivariate analysis provides a robust framework for evaluating soil quality and supports management strategies aimed at improving soil structure and carbon stabilization.