Soil Aggregate Stability and Carbon Distribution for Sustainable Carbon Management

ABSTRACT Soil aggregates play a critical role in regulating the stabilisation and persistence of soil organic carbon (SOC), yet the influence of different land use systems (LUS) on aggregate associated SOC dynamics in tropical soils remains poorly quantified. This study examined aggregate stability and the distribution of aggregate‐associated SOC across five LUS: natural forest (NF), rubber plantation (RP), coconut plantation (CP), vegetable field (VF) and paddy field (PF), in the humid Palakkad Central Plain of Kerala, India. Soil samples were collected from two depths (0–20 cm, 20–40 cm) across the five LUS. Surface and subsurface samples were analysed for water stable aggregate fractions, stability indices (MWD, GMD), aggregate size distributions viz .macroaggregates (> 0.25 mm), micro aggregate (0.053–0.25 mm) and clay and silt‐sized aggregate fraction (< 0.053 mm) and their associated SOC per cent stored within macro, micro and clay & silt aggregates. NF and RP showed the highest macroaggregate proportions, aggregate stability and aggregate‐associated SOC, whereas VF and PF exhibited pronounced aggregate breakdown and reduced SOC due to intensive tillage and puddling. The substantially higher microaggregate‐associated SOC in NF, compared with PF, demonstrates the efficient change of carbon into long‐term stabilisation pathways only when aggregate integrity is maintained. The study reveals that long‐term carbon stabilisation in tropical soils depends more on the soil's structural stability and aggregate turnover pathways than on carbon inputs alone.