Fertility and desorption capacity of Anthrosols (Archaeological Dark Earth - ADE) in the Amazon: The role of the ceramic fragments (sherds)

Numerous patches of black soil can be found throughout the Amazon basin, primarily along the margins of rivers. This type of soil is known as Archaeological Dark Earth (ADE) and is formed as a result of prehistoric human occupation and classified as Anthrosols. The chemical characteristics of ADE are distinct from those of the region's predominant soils, making them popular with local subsistence farmers. The patches of ADE are characterized by an abundance of ceramic fragments (sherds) (CF) both on the surface of the patches and within their inner depths. Considering that these sherds are generally composed of quartz, metakaolinite, feldspars, non-plastic materials, often with high levels of aluminum phosphates, the present study focused on their potential contribution to maintenance to the fertility of ADE soils, under the conditions of tropical weathering. With this aim, the mineralogical composition of the sherds was obtained using X-ray diffraction with the support of SEM-EDS readings. In addition, some parameters of fertility were measured as well as phosphates dissolution in the presence of citric acid as a function of time. The nutrients and micronutrients were determined by atomic absorption spectrometry and the molybdenum blue method. The results showed that the fragments analyzed were composed of quartz, feldspars, metakaolinite, micas/illites, and anatase, but differ in the presence/absence of chlorites, talc, cristobalite, and calcites. This study characterized the sherds as highly fertile and provides experimental confirmation that the sherds release phosphor under conditions approximating the natural weathering environment, which indicates that they are an important potential source of nutrients.