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|Type:||Artigo de periódico|
|Title:||Distribution And Biogeochemistry Of Inorganic Chemicals Associated With Forest Conversion And Pasture Installation In Rondônia (brasilian Amazon Basin)|
|Abstract:||Forest burning for pasture installation in tropical areas represents an important component on biogeochemical cycles. In order to get information about modifications within the element composition after forest burning, in this local study the attempt has been undertaken to provide a first overview about the total contents of a larger set of elements (29) and their distribution patterns in topsoils when forest is shifted for pasture use. The work was carried out in 1999 in Rondônia state (Brazilian Amazon Basin) focussing on a native forest site and 4 neighbouring pastures established in 1987, 1983, 1972 and 1911 after forest conversion. Mostly higher values of nearly all investigated macro- and micro-nutrients, but also of other elements (e.g Sr, Cr, Ni, V or Pb) as well as increases of pH levels could be determined twelve years after forest burning in the pasture of 1987. Conversely, pH values of pH 7.6 five years after forest clearing in pasture 1987 (0-5 cm) and pH 5.5 in the same pasture after 12 years suggest a loss of basic acting cations in the present sandy soils due to high rainfall intensities. After initial element increases in pasture of 1987 the decreases of main nutritional elements (e.g. C, N, K, S) in the pasture of 1983 as well as again the enhanced levels in pasture 1972 and 1911 suggest both a persistent leaching and a function of pasture age where external element inputs exceed outputs. Ash deposition, animal excreta, accumulation of organic matter as well as natural soil conditions are discussed as influencing factors on the measured element budgets. Chemical fingerprint graphs of the pasture soils related to the chemical conditions in the forest soil illustrated different element distributions in the pastures. Nevertheless, in this particular area it can be suggested that continuous pasturing after forest clearing primarily enriched the soils in elements. From the ecotoxicological aspect the results showed low risks of toxic elements in the considered area compared to element ranges for unpolluted soils.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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