Chemical characteristics of Amazonian Dark Earth in Santarem, Brazil

This research aimed at to compare some chemical characteristics (pH in water, and KCl, Ca2+,Mg2+, K+,Al3+, organic phosphorus 'P-org' and available phosphorus 'P-ava') of anthropogenic and non-anthropogenic soils. Soil samples were collected at five depths: 0-20, 20-40, 40-60, 60-80 and 80-100 cm in two archaeological sites and one non-anthropogenic area. The analysis revealed that the anthropogenic soils presented higher amount of P-ava than the non-anthropogenic ones, and that these amounts presented a positive correlation with the Ca2+ contents, which reflects the incorporation of animal bones, mainly fish to these soils. However, the non-homogeneous distribution of these species and the low K+ contents found in most samples may be limiting for some cultures. Finally, it was possible to differentiate samples of the anthropogenic soils from non-anthropogenic ones by using the values of pH in water and KCl, as well as the P-org and P-ava contents.