Impact of livestock grazing on soil potential net C and N mineralization during the dry season in a cultivated subhumid tropical grassland ecosystem

Cultivated tropical grasslands have been hypothesized to have great soil carbon (C) and nutrient storage potential. However, global change and the resulting seasonal soil drying–wetting shifts may affect this potential. Limited data exist to predict the biogeochemical responses of these ecosystems under different management and climate conditions. Our objectives were (1) to explore the relationship between total and available C, nitrogen (N), and phosphorus (P), microbial biomass C, and C and N transformation in surface soil during the dry season under the two livestock species influence (water buffaloes [WB]; and Nellore cattle [NC]) and (2) to explore the livestock species effect on soil C transformation patterns across time and during a water pulse in the dry season. The results suggest that there is a seasonal pattern response and a differentiation in soil microbial activity shaped by livestock type and soil wetting. Furthermore, a high potential net C mineralization rate (PNCMR) (20.03 ± 1.13 μg C g⁻¹ d⁻¹) and retention of ammonium (0.04 ± 0.005 mg g⁻¹), nitrate (0.04 ± 0.005 mg g⁻¹), and soluble P (12.51 ± 0.9 μg g⁻¹) appear to be associated with the ecosystem with WB. In the case of NC, a lower PNCMR (9.54 ± 0.60 μg C g⁻¹ d⁻¹) and high N mineralization (84.34 ± 12.35 μg g⁻¹) may promote N losses in dry soil. These results could help to better understand the conservation and soil nutrient availability of complex grazing ecosystems in the subhumid tropics.