Chemical and physical properties of an anthropogenic dark earth soil from Braganca, Para, Eastern Amazon

Abstract

Although anthropogenic dark earth (ADE) is generally found in non-floodable land, it also occurs on floodplains but, there is no information about the chemical and physical characteristics of ADE in this environment. In this study, we propose to check the hypothesis that a Gleysol, classified as ADE, presents improved chemical and physical conditions than an adjacent soil, no anthropogenic. Thus, the objective of this study was to characterize the chemical and physical properties of the top layer of two ADE profiles in a Gleysol and compare them with an adjacent soil. Samples were taken from two areas classified as ADE in Braganca, Para State, Brazil, at the Jabuti archaeological site, and from an adjacent non-anthropogenic site. Disturbed and undisturbed soil samples were collected at the soil depth of 0.05-0.10 m for chemical (pH, potential acidity, exchangeable cations, and soil organic carbon) and physical (soil particle size distribution, particles density, water retention curve, total porosity, microporosity, macroporosity, and bulk density) analysis. 'The two areas of ADE in a Gleysol, showed improved soil chemical properties compared to the adjacent soil, particularly in relation to phosphorus and calcium levels that contributed to higher cation exchange capacity which, in turn, was positively related to organic carbon content. Changes in soil physical properties were less noticeable but both areas of ADE presented higher water retention capacity, particularly at low tension. The improved conditions of the ADE soil under Gleysols shows that these areas are adequate for soil cultivation, especially with plants adapted to floodplain.