ABSTRACT The activities of people who lived on the Brazilian coast since the Holocene have mainly determined the formation of Sambaqui (= shell mound) soils. Residues from shells and other animals and plants used as food by these people were deposited, resulting in soils with high levels of phosphorus (P) and organic carbon, as well as high base saturation. This study aimed to evaluate P fractions, establish possible relationships between P measurement methods in the soil profiles of Sambaqui formations, and contribute to the definition of a soil class in the Brazilian Soil Classification System (SiBCS) that describes anthropogenic pedogenesis. Three soil profiles with records of anthropogenic activity were selected and sampled for this study, all in São José de Ribamar, Maranhão, Brazil. Soil morphology was described, the physical and chemical properties of the horizons were analyzed, and the profiles were classified according to the SiBCS. Available P was extracted by different methods, and P was fractionated. Surface horizons of profiles P2 and P3 were identified as anthropogenic A, with dark colors, presence of shells, high calcium and organic carbon concentrations, high base saturation, and P content greater than 30 mg kg -1 of soil. Of the available P extractants, Mehlich-3 withdrew the highest P concentrations. Olsen method was positively correlated with pH values, shell presence, and calcium carbonate levels. Phosphorus fractionation of the studied profiles indicated highest representation of the occluded and available P fractions (Mehlich-3). According to the SiBCS, the profiles were classified as Cambissolo Háplico Carbonático (P1 and P3) and Cambissolo Háplico Ta Eutrófico (P2), and an anthropogenic subgroup was proposed for P2 and P3. Based on the World Reference Base (WRB), the profiles were classified as Pretic Calcaric Cambisol (P1) and Pretic Anthrosols (P2 and P3). In other words, the WRB classifies these soils at a high hierarchical level (as Anthrosols or by the main qualifier Pretic), in contrast with the SiBCS.
Alves et al. (Thu,) studied this question.