Changes in soil labile inorganic phosphorus and fertility over time after agricultural land-use in the Cerrado of Northeastern Brazil

Land-use change in tropical environments significantly affects soil nutrient dynamics, particularly phosphorus (P). This study aimed to evaluate the effects of agricultural conversion and different years of land-use on soil chemical attributes and inorganic phosphorus fractions in the Brazilian Cerrado. Six areas were selected, forming a chronosequence ranging from 1 to 20 years of soybean-based agriculture, including a reference site under degraded pasture. Soil samples (0.0–0.20 m) were analyzed for pH, organic matter, exchangeable bases, and P fractions using a sequential extraction method. Data were subjected to analysis of variance and multivariate analysis (principal component and cluster analysis). Results showed increases in soil pH and base saturation over time, likely due to liming and fertilization practices. The long-term (Y17) agricultural use significantly increased (p < 0.05) the labile P fraction (P-Al) to 365 ± 16 mg kg⁻¹, while moderately labile and non-labile fractions remained stable or increased slightly. These findings suggest that agricultural use alters P availability by promoting the accumulation of residual P and its gradual conversion into less available forms. Although site variability in management history limits broad conclusions, the study provides evidence of P dynamics in tropical systems and reinforces the importance of monitoring P fractions in long-term agricultural soils.