Abstract
Soils with an A horizon formed by human activity, an anthropogenic A horizon, are found in the Amazon Region. Few studies have examined the spatial distribution of the properties of these soils. We mapped the spatial variability of some soil properties in an area of Archaeological Dark Earth (ADE) in the Brazilian Amazon. A sampling grid was defined over an area of 42 × 88 m under cacao cultivation in which sampling points were established at a spacing of 6 × 8 m, for a total of 88 points. Samples were collected from the 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.30 m depth layers. Soil texture, aggregate stability, and organic carbon (OC) analyses were performed on disturbed soil samples. Undisturbed samples were used to determine soil macroporosity (Macro), microporosity (Micro), total porosity (TP), and soil resistance to penetration (RP). The results were analyzed by descriptive statistic, Pearson correlation (p<0.01), and geostatistics. Soil bulk density, total pore volume, and geometric mean diameter are dependent on the total amount of OC in the ADE area. Increased soil bulk density and RP are proportional to a decrease in OC content and lower Micro and TP. Moreover, soil resistance to penetration is influenced by soil water and clay content with depth.
Highlights
The different types of soil in the Amazon region include soil with an anthropogenic A-horizon, i.e., formed by human activity (Santos et al, 2013b)
Total pore volume, and geometric mean diameter are dependent on the total amount of organic carbon (OC) in the Archaeological Dark Earth (ADE) area
According to the coefficient of variation (CV) classification proposed by Warrick and Nielsen (1980), who classified CV 60 % as high variability, we noted that part of the properties studied showed low variability, except for Geometric mean diameter (GMD), Macro, resistance to penetration (RP), sand and clay contents for all soil layers, Micro for the 0.00-0.05 m layer, and bulk density (BD) for the 0.20-0.30 m layer, which showed medium variability
Summary
The different types of soil in the Amazon region include soil with an anthropogenic A-horizon, i.e., formed by human activity (Santos et al, 2013b). These soil units, known as Dark Earths, Indian Dark Earths, or Archaeological Dark Earths (ADEs), generally stem from ancient Indian settlements, and stand out through the presence of ceramics and cultural artifacts, as well as dark color and large deposits of stable organic matter (Campos et al, 2011). ADEs are naturally fertile, with high levels of phosphorous, calcium, magnesium, and stable organic matter and greater biological activity compared to surrounding soils (Glaser, 2007). Organic matter contents play other vital functions in the lifecycle, ranging from microbial and soil fauna activities to positive action on aggregate stability, soil porosity, and soil density, contributing to reduce soil compaction (Spera et al, 2010)
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