Spatial variability of soil physical properties in Archeological Dark Earths under different uses in southern Amazon

The Amazon region has soils of an anthropic formation called Anthropogenic Dark Earths (ADEs). These soils present a higher fertility and are physically different to adjacent local soils. This study aimed to investigate the conditions and spatial behavior of soil physical attributes in ADE areas cultivated with cocoa, coffee, and grassland in southern Amazon. Mapping of three ADE areas was carried out by using sampling grids of 80 m x 56 m with regular spacing of 8 m for the grassland area and 48 m x 88 m with a spacing of 6 m x 8 m for the cocoa and coffee areas. These soils were sampled at the grid crossing points at depths of 0.00-0.05; 0.05-0.10 and 0.10-0.20 m, totaling 88 points in each area. Soil physical analyses of texture, macroporosity, microporosity, total porosity, bulk density, theta FC (moisture field capacity), penetration resistance, and aggregate stability were carried out. The data were submitted to descriptive statistics, geostatistics, and multivariate statistics. In the ADE area cultivated with grassland, the attributes showing moderate and weak levels of spatial dependence were those with a greater spatial continuity, i.e. texture, penetration resistance, macroporosity, microporosity, and volumetric moisture. A similar behavior was observed in the ADE areas cultivated with coffee (sand, density, penetration resistance, macroporosity, and microporosity) and cocoa (silt, clay, penetration resistance, macroporosity, and mean weight diameter of aggregates).