Soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest in southwestern India

•SOC stocks in soils in southwestern India range from 58.2 to 169.4 Mg C ha−1 in 0–60 cm.•Subsoil contribution (>30 cm) to profile SOC stock (0–60 cm) can be up to 40%.•Differences in SOC stocks depend on vegetation type, geology and soil properties.•TOC, 13C, C:N and mid-infrared are good proxies for vegetation and SOC dynamics.