Effects of grazing intensity and pasture type on soil organic carbon stock in the semi-arid tropics of India

Pastures may act as carbon sources and sinks depending on grazing pressure and management practices. Soil organic carbon (SOC) stock and its fractions were quantified under 3 different grazing intensities using 5, 10 and 15 sheep/ ha under sown, improved and natural pastures in the semi-arid tropics of India. Results revealed that after 3 years, improved pasture had significantly higher particulate organic carbon (POC-4.5 g/kg), SOC (-0.53 %), total organic carbon (TOC-7 g/kg) and SOC stock (-15 mg/ha) as compared with sown and natural pastures. Labile carbon (LC -185 mg/kg) and soil microbial biomass carbon (SMBC -378 mu g/g soil) were higher under natural pasture. A moderate grazing intensity of 10 sheep/ha resulted in significantly greater carbon fractions, TOC and SOC stock. SOC stock and its fractions were significantly higher in the topsoil layers as compared with the subsoil layers. These results indicate that improved pasture management practices with moderate grazing intensity can be recommended for improving SOC stock and its fractions in semi-arid tropical pastures.