Soil nutritional sustainability in Cerrado Oxisols using a fuzzy index (FSNSI)

The conversion of natural ecosystems into agricultural and silvicultural systems reshapes organomineral stabilization kinetics and, consequently, nitrogen and phosphorus stocks in Cerrado Oxisols. This study proposes the Fuzzy Soil Nutritional Sustainability Index (FSNSI) as a decision-support tool that integrates chemical capital, expressed as N and P stocks, and physical constraint, expressed as soil bulk density, into a scalable metric for the production phase in life-cycle sustainability assessment. Compositional partitioning indicated the dominance of humic fractions relative to the total, with a median humic contribution of 76.0% for N, and a low contribution of labile fractions, with a median of 12.18%, supporting a retention regime controlled by recalcitrant reservoirs. Native vegetation showed the highest humic contribution, with a median of 82.0%, and the lowest residual fraction (4.96%), whereas agriculture showed a reduced humic contribution (median 73.0%) and an increased residual fraction (17.15%), suggesting a greater allocation of mass into compartments not recovered by the operational extractions. Forest plantations showed a median total nitrogen stock per layer of 1.362, approximately 21.2% higher than native Cerrado, while maintaining a humic-dominated stabilization regime. The FSNSI discriminated land uses (Gamma GLM with bootstrap resampling, n = 1000), with higher functionality in Eucalyptus (Exp(B) = 6.07), followed by native Cerrado (Exp(B) = 4.42), indicating that functional performance may be optimized when continuous organic inputs occur without recurrent mechanical disturbance. We conclude that the co-stabilization of N and P in humic fractions, modulated by the physical integrity of the soil, is the central mechanism sustaining nutritional functionality in highly weathered tropical environments, and that FSNSI provides an integrated metric to guide interventions, prioritization, and routine environmental monitoring and assessment in land-management programs.