Quasi-equilibrium of organic carbon in shrink-swell soils of the subhumid tropics in India under forest, horticulture, and agricultural systems

Restoration of soil quality through soil organic carbon (SOC) management has been a major concern for tropical soils. SOC is sensitive to human activities such as deforestation, biomass burning, land-use changes, and environmental pollution. Our aim in this study was to elucidate the effect of land-use systems on quasi-equilibrium values (QEV) of SOC. To determine the QEV of SOC, 4 representative pedons from Nagpur district, Maharashtra, under horticulture (orange), agriculture (cotton, cotton + pigeonpea), and forest (teak) with the time of cultivation ranging from 20 years to centuries were selected. The study indicated that the QEV of SOC in the shrink-swell soils decreased when they were used for agricultural crop production. Since all these soils have similar substrate, the SOC equilibrium values obtained in soils of horticultural and forest ecosystems may also be attainable in the soils under agricultural system. In other words, addition of external sources of farmyard manure or other green manure may raise the QEV of SOC from 0.44-0.51% to 0.70-0.80% in soils of agricultural system.