Summary
This field study challenges the widely-held assumption that increasing fine mineral particle content enhances soil organic carbon storage in high-clay soils. Contrary to expectation, SOC was poorly related to fine fraction content across a range of Vertisols, and increasing fine fraction did not improve SOC retention under long-term cropping. The findings suggest that in these fine-textured soils, particulate organic matter management may be more critical than mineral surface area for maintaining carbon in the mineral-associated fraction.
UK applicability
UK clay-rich soils share similar mineralogical properties with Vertisols, so the finding that fine fraction content alone is not a reliable predictor of SOC storage has potential relevance for UK soil management and policy. However, the subtropical climate, land use history, and specific Vertisol properties of the study sites may limit direct transferability to cooler, wetter UK conditions.
Key measures
Fine fraction content (481–927 g kg⁻¹), soil organic carbon pools (fPOM, oPOM, fine-MAOM), specific surface area, SOC coverage on mineral surfaces (%), paired native and cropped soil comparisons
Outcomes reported
The study quantified soil organic carbon (SOC) storage across paired native and cropped Vertisols in relation to fine fraction mineral content (soil particles < 53 µm), measuring free particulate organic matter, occluded POM, and fine mineral-associated organic matter using density and particle-size fractionation.
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