Soil Organic Carbon Fractions and Fertility Across Degraded, Forest, and Restoration Areas in Desertification Hotspots of the Brazilian Semiarid Region

Soil carbon dynamics and fertility may respond differently to land-use systems in the Brazilian semiarid region due to its high environmental and edaphic heterogeneity. This study evaluated soil attributes in degraded, forest, and restoration areas across the states of Ceará (CE), Paraíba (PB), Pernambuco (PE), and Piauí (PI). Surface soil samples (0–10 cm) were analyzed for particle-size distribution, pH, total organic carbon (TOC), humic fractions, available phosphorus, exchangeable cations, and cation exchange capacity (CEC). Soil responses to land use varied markedly among states. Forest areas showed 12% and 57% higher TOC than degraded areas in PB and PI, respectively. Restoration areas showed substantial changes in specific carbon fractions; in PB, humic acid carbon was approximately 85–95% higher and humin carbon 136% higher than in the degraded area. Available phosphorus was also markedly higher in restoration areas in PB and PI. In PI, the restoration area was characterized by high Ca²⁺ and Mg²⁺ contents and CEC, whereas soil pH ranged from approximately 5.0 in the forest area to 8.0 in the degraded area. Overall, restoration areas showed improvements in specific soil attributes, although the magnitude and direction of these responses were strongly modulated by local edaphic conditions.