Physico-chemical properties and their variation of amazonian dark earths distributed in middle Amazon basin, Brazil
2007
Nakamura, S.(Tsukuba Univ., Ibaraki (Japan)) | Hiraoka, M. | Matsumoto, E. | Tamura, K. | Higashi, T.
The most widely distributed soil in the Middle Amazon basin is the Yellow Latosol (YL). However, a dark soil with a fertile surface known locally as Amazonian Dark Earths or Terra Preto do Indio (TP) is found scattered in many places of the Amazon basin (Sombroek, 1966) . It has been shown that the surface of the TP is characterized by high phosphate content, exchangeable Ca, humic substances, and anthropogenic ceramics. These facts seem to indicate that soil amelioration was accomplished by the prehistoric Amerindian population. To this date, however, a detailed pedogenesis process of TP has not been carried out. In particular, the accumulation process of soil organic matter in TP is one of the most important issues regarding its genetic process. The primary objective in this study was to compare the physico-chemical properties of TP and adjacent soils, and to investigate the variation of TP in the middle Amazon basin. In the study area, soil textures were variable among TP in different sampling sites, probably caused by the sedimentary environment of parent materials. All TP had a granular structure in surface black horizons. The chemical properties of TP had significant correlation with clay contents; namely, TP with fine texture showed diagnostic properties indicated by higher contents of P, exchangeable Ca, total carbon, etc., while this tendency was not so evident in TP with coarser texture. However, variation in P and exchangeable Ca contents among different sampling sites was large to encounter the difference in the texture. It was shown that the chemical properties of TP were largely determined by their soil texture, particularly clay contents, but the impacts of anthropogenic effect were also partly taken into consideration.
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