Pasture soil carbon stock: comparison with disturbed Atlantic Forest and impact of improved management

This study investigated how the conversion of disturbed Atlantic Forest remnants to pastures, followed by pasture intensification, affects soil carbon (C) stocks and sequestration potential in São Paulo State, Brazil. Three forest–pasture pairs located on contrasting soils (two clayey Oxisols and one medium-textured Ultisol) were evaluated, combined with grazing and fertilization experiments under non-rotational and rotational dairy and beef systems. Forest–pasture comparisons showed that land use conversion increased soil bulk density, indicating cattle-induced compaction. Forests exhibited higher C and N concentrations, particularly in surface layers, associated with continuous litter deposition, chemically recalcitrant biomass, preserved soil structure, and greater biological activity. In contrast, pastures showed lower C and N concentrations, particularly at the RU-NO site (Ultisol). Responses of cumulative soil C stocks varied among sites. In one clayey Oxisol, pasture soils exhibited greater C stocks at 40–100 cm than forest soils, likely associated with deep Urochloa rooting and organomineral stabilization. Conversely, forest-to-pasture conversion reduced soil C stocks down to 100 cm in the Ultisol and in the second Oxisol, indicating greater susceptibility to C losses under low-input pasture systems. Natural-abundance δ 13 C profiles revealed predominance of C₄-derived carbon in pasture soils and mixed C₃–C₄ signatures in forest areas, reflecting historical land-use dynamics and legacy effects. Improved pasture management increased soil C stocks in the 0–30 cm layer within two years. Non-rotational systems showed C accumulation rates ranging from 3 to 6 t C ha -1 yr -1 , whereas rotational systems accumulated between 1 and 4 t C ha -1 yr -1 . Land- use change factors for the 0–30 cm layer were close to the IPCC reference value (1), although contrasting responses were observed when deeper soil layers were considered. Overall, low-input pasture systems promoted reductions in soil C stocks, whereas improved pasture management, including fertilization, legume integration, and grazing control, enhanced soil C accumulation, particularly in clay-rich soils.