Acidez e manejo da fertilidade em solos amazônicos: estudo em áreas da planície do Rio Madeira, AM

Abstract

Amazonian soils are mostly characterized by a high degree of weathering, high acidity, low nutrient contents, and high aluminum saturation, which limit their natural fertility and agricultural use. In this context, this study aimed to evaluate soil acidity in soils from the Madeira River floodplain, in the municipality of Humaitá, Amazonas, and to suggest management strategies to improve soil fertility. A total of 25 soil samples were analyzed and subjected to chemical and physical analyses, including pH, exchangeable cations, potential acidity, organic carbon, and derived attributes such as base sum, cation exchange capacity, base saturation, and aluminum saturation. The results showed strongly acidic pH values, high levels of exchangeable aluminum, high aluminum saturation, and low base saturation, confirming a chemical environment restrictive to crop development. Cor-relation analyses indicated negative relationships between pH and Al³⁺, as well as be-tween aluminum saturation (m%) and base saturation (V%), and positive correlations among basic cations, cation exchange capacity, and base saturation, evidencing the antagonism between aluminum and exchangeable bases in the exchange complex. Organic carbon contributed positively to cation exchange capacity and partially mitigated potential acidity, although it was insufficient to neutralize the intensity of the observed acidification. It is concluded that improving the fertility of the evaluated soils depends on the adoption of integrated management practices, including liming to correct surface acidity, agricultural gypsum application to improve chemical conditions at depth, and conservation practices that promote organic matter accumulation, aiming at the sustainability of agricultural systems in the Amazon region.