Impactos no uso e manejo do solo sobre as propriedades hidráulicas no Sul do Amazonas, Brasil

Abstract

The replacement of forests by agricultural or pasture areas alters the physical attributes of soils, increasing bulk density and reducing organic matter content. Understanding these effects is essential for conserving soil and water resources and promoting sustainable agricultural systems. This study aimed to analyze the impacts of land use and management on the physical and hydraulic properties of soils under different land-use systems in southern Amazonas, Brazil, including native forest, pasture, açaí (Euterpe oleracea) cultivation, and cassava (Manihot esculenta). Field and laboratory methods were applied, including tests for aggregate stability, soil penetration resistance, porosity, texture, and water infiltration. The evaluated attributes included bulk density (BD), soil penetration resistance (SPR), volumetric (θv) and gravimetric (θg) moisture, aggregate distribution, infiltration, and parameters of water retention and hydraulic conductivity curves. Water retention analyses were performed at matric potentials of −1, −3, −6, −10, −30, −50, −75, −1000, and −1500 kPa, fitted using the van Genuchten model. Results showed that BD increased with depth, ranging from 1.25 to 1.45 g cm⁻³, with higher values under açaí and cassava, indicating moderate to high compaction. SPR exceeded 3.0 MPa in pasture (0–20 cm), a critical threshold for root growth, while remaining below 1.5 MPa in forest soils, reflecting better structure. The mean geometric diameter (MGD) and mean weight diameter (MWD) ranged from 1.1 to 2.8 mm, with greater stability under forest. Saturated hydraulic conductivity (Ks), modeled using van Genuchten– Mualem, varied from 25.70 mm h⁻¹ (cassava) to 81.22 mm h⁻¹ (pasture), indicating strong influence of pore structure and connectivity. It was concluded that intensive land use and inadequate management, particularly in pasture and cassava areas, promote physical degradation and reduce hydraulic functionality, whereas forest and perennial açaí cultivation help preserve the structural and hydrological quality of Amazonian soils.