Long-Term Grazing Mediates Soil Organic Carbon Dynamics by Reorienting Enzyme Activities and Elemental Stoichiometry in Semi-arid Tropical Inceptisol

Long-term grazing by small ruminants diminishes grass and plant covers, alters various biophysical situations and nutrient stoichiometry and modifies soil enzyme activity, and is therefore vital for nutrient cycling in the ecosystem. To apprehend the link between grazing, soil organic carbon (SOC), nutrient cycling enzyme, nutrient stoichiometry and nutrient availability, a grazing study was conducted with 3 different stocking rates (SR1 = 1 adult cattle unit (ACU) ha −1 , SR2 = 2ACU ha −1 and SR3 = 3ACU ha −1 ) in 5 ha of pasture lands and was compared with a control at 5% level of significance under randomized block design. Soil samples were collected from surface and subsurface layers and analysed for SOC and nutrient cycling enzyme, nutrient stoichiometry and their plant availability. In general, pasture productivity under SR1 was significantly higher than SR2 and SR3. SR2 and SR3 significantly depleted SOC (by ~ 20%), nitrogen and sulphur concentration than SR1 and control ( P ≤ 0.05) without affecting phosphorus availability. Generally, grazing diminished particulate organic matter-associated C (POMC); however, SR1 significantly increased mineral associated C (MOMC). Grazing significantly altered nutrient stoichiometry in all the soil layers. High grazing pressure significantly reduced dehydrogenase, sulfatase and urease activities over control; however, SR1 boosted activities of phenoloxidase (33%) and peroxidase (32%) over control. Despite that, SR1 recorded ~ 25% lower carbon loss than control; however, SR2 and SR3 had similar carbon loss to control despite having lower SOC in the upper soil layer. Grazing augmented C decay rate (kc) by > 69 and 32% over control in those soil layers, respectively. Grazing with moderate to high stocking rate had a negative impact on SOC, its pools and nutrients. Low stocking rate, i.e., SR1, would sustain SOC and nutrient concentration, and maintain productivity, and hence, could be adopted in the semi-arid tropical regions.