Physical-hydric attributes in areas under forest-pasture conversion in southern Amazon, Brazil
Authors: Almeida Romária Gomes de , Campos Milton César Costa , Silva Douglas Marcelo Pinheiro da , Santos Robson Vinício dos , Lima Alan Ferreira Leite de , Souza Renato Francisco da Silva , Bezerra Francilel Arruda , Dias Thiago Jardelino , Oliveira Flávio Pereira de 
Published: November 2024

Description of the subject. The increasing occupation and exploitation of the Amazon has resulted in the increased conversion of forest areas into agricultural land or pasture. This often has negative impacts on soil and water dynamics. Therefore, there is a need for comparative studies between forest areas and those undergoing pasture conversion, in order to provide information to mitigate the impacts caused. Objectives. This study aimed to evaluate the physical and hydrological attributes of areas where forest has been replaced by pasture, located in the southern Amazon, Brazil. Method. The study areas are located in Humaitá, in the southern Amazon. For this study, five pasture areas, one natural pasture area, and one forest area were selected. A transect was established in each area containing fifteen sampling points. Mini trenches were opened at each point to collect soil samples (disturbed and undisturbed) in the 0.00-0.10 and 0.10-0.20 m depth. The samples collected in clods were dried in the shade and then crushed to obtain fine air dried soil. The volumetric rings (undisturbed samples) were saturated on the tension table and finally subjected to a penetrograph. Soil attributes such as sand, silt, clay, macroporosity, microporosity, total porosity, volumetric soil water content, and soil penetration resistance were also determined in the laboratory. The data obtained was tabulated and analyzed using descriptive statistics, a test of means to group the different environments, correlation analysis, and principal component analysis using multivariate analysis. Results. The results indicate that the conversion from forest to pasture harmed soil penetration resistance, volumetric soil water content, total porosity, and soil macroporosity. Pearson correlation in the first depth (0.00-0.10 m) revealed that sand content negatively correlated with microporosity, total porosity, and silt but no correlation with the other attributes. The soil penetration resistance showed a negative correlation with macroporosity, total porosity, and volumetric soil water content, suggesting a direct relationship where changes in the volumes of macroporosity, total porosity, and volumetric soil water content can significantly affect the soil penetration resistance. In the 0.10-0.20 m depth, the soil penetration resistance correlated negatively with macroporosity and positively with microporosity. The total porosity, correlated positively with microporosity and macroporosity and negatively with sand content. In this depth, macroporosity showed no correlation with microporosity. Conclusions. The forest and natural grassland areas stood out for having higher volumetric soil water content, microporosity, and total porosity, while the pasture areas were characterized by high penetration resistance. Amazonia, soil, environmental impact assessment, soil quality