Fertilidade natural de argissolos alumínicos no sul do Amazonas: controles pedogenéticos, edáficos e limitações químicas

Abstract

Argissolos Alumínicos are among the predominant soil classes in southern Amazonas and exhibit chemical constraints resulting from intense weathering and base leaching, which limit their agricultural potential. This study aimed to evaluate the natural fertility of Argissolos Alumínicos in southern Amazonas by identifying the pedogenetic and edaphic controls responsible for the variability of their physical and chemical attributes and for the main constraints affecting nutrient availability. Sixteen diagnostic horizons from three Argissolos Alumínicos profiles representative of different phytophysiognomies were analyzed and classified according to the Brazilian Soil Classification System (SiBCS). Particle-size distribution, soil organic carbon, pH, available phosphorus, exchangeable cations, potential acidity, cation exchange capacity, and fertility indices were determined. The data were subjected to descriptive statistics, the Shapiro–Wilk normality test, Spearman's rank correlation, and hierarchical cluster analysis. The results revealed high soil acidity (pH_H₂O = 3.55), low base saturation (9.16%), high aluminum saturation (86.29%), low available phosphorus contents, and low concentrations of exchangeable bases, confirming the dystrophic nature of these soils. The vertical distribution of soil attributes indicated an increase in clay content in the subsurface horizons associated with clay lessivage, as well as higher soil organic carbon concentrations in the surface horizons resulting from plant residue cycling. Soil organic carbon showed a strong positive association with fertility indicators and a negative association with aluminum saturation, whereas multivariate analysis revealed two major environmental gradients related to soil fertility and soil acidity, respectively. It is concluded that the natural fertility of Argissolos Alumínicos is primarily controlled by the interaction among soil organic matter, base availability, and soil acidity, with high aluminum saturation and low phosphorus availability representing the main chemical constraints. These findings provide a scientific basis for management strategies focused on acidity correction, soil organic matter conservation, and the sustainable use of Amazonian soils.