In tropical and subtropical soils, sesquioxides and soil organic matter (SOM) are major binding agents for aggregates. However, the biotic and abiotic contributions to aggregation are often difficult to distinguish. In this study, we attempted to assess their contributions to aggregation separately, as indicated by aggregate size distribution and specific surface area (SSA). Our objectives were (i) to determine aggregate size distribution and SSA before and after removal of sesquioxides and SOM, and (ii) to assess the contributions of sesquioxides and SOM to soil aggregation. An oxide-rich Ult...