Soil functioning indicators decline with land-use intensification in the Peruvian Amazon: evidence from Ucayali

Abstract

Rapid land-use change in the Peruvian Amazon threatens soil processes that sustain productivity and ecosystem resilience. This study assessed soil functioning indicators along a land-use intensification gradient in Ucayali, Peru.Methods: We evaluated physicochemical (texture fractions, pH, organic matter, cation-exchange capacity, carbon, and micronutrients) and biological indicators (cultivable microbial groups, microbial biomass carbon, respiration, and macrofauna) from 54 independent composite topsoil samples (0–20 cm) across seven land-use systems, multiple localities, and soil texture classes. Principal component analysis and univariate tests were applied to identify multivariate gradients and significant differences among groups. PCA revealed a dominant texture–fertility gradient contrasting sand-rich soils with finer-textured soils associated with higher CEC, organic matter, total carbon, and micronutrients (notably Mn and Cu). Significant differences among land-use systems were detected for CEC, OM, Mn, pH, Cu, SOC, and sand. Cacao agroforestry differed from pasture and oil palm systems in key fertility indicators. Biological indicators showed weaker global separation, although macrofauna differed significantly among land uses. Soil texture modulated baseline fertility and the expression of land-use impacts. Cacao agroforestry and secondary forests occupied transitional positions between forests and intensive systems. A reduced monitoring set including texture fractions, OM, CEC, pH, Mn, and selected biological metrics is recommended for tracking soil degradation in heterogeneous Amazonian landscapes.