FOREST LITTER DECOMPOSITION AS AFFECTED BY EUCALYPTUS STAND AGE AND TOPOGRAPHY IN SOUTH-EASTERN BRAZIL1

Forest litter decomposition is a major process in returning nutrients to soils and thus promoting wood productivity in the humid tropic. This study aimed to assess decomposition of eucalypt litter in the Rio Doce region, Brazil. Leaf litter was sampled under clonal eucalypt stands aged 2, 4 and 6 years on hillslopes and footslopes. Soil and soil+litter samples were incubated at two levels of soil moisture, temperature and fertilization. C-CO2 emissions from soil measured during 106 days were higher at 32 °C than at 23°C, mainly for the 2-yr-old stand on footslope. When leaf litter was added on soils, C-CO2 emissions were eight times higher, mainly on footslopes, with no effect of stand age. Leaf decomposition in situ, assessed with a litterbag experiment showed a mean weight loss of at least 50% during 365 days, reaching 74% for 2 yr-old stands on footslopes. In comparison with data from the native forest and the literature, no apparent restrictions were found in eucalypt litter decomposition. Differences between in vitro and in situ results, and between eucalypt and native forest, were most likely related to the response of diverse decomposer communities and to substrate quality

Xanthic- and Rhodic-Acrudoxes under cerrado vegetation: differential internal drainage and covarying micromorphological properties

ABSTRACT Soil internal drainage plays a major role in soil genesis, and it is mostly dependent on topography. However, the existence of sedimentary and meta-sedimentary rock strata with variable dip angle allows for strong differences in internal drainage for identical topographies, which result in a marked differentiation in the properties of overlain soils. This work aimed to investigate the micromorphology of soils formed from different dip angles of rock strata and their relationships to internal drainage, in Minas Gerais, Brazil. Over horizontal strata, a Xanthic Acrudox lacking hematite and with blocky structure has developed. Over strata with 45° dip angle, strong drainage has resulted in intense desilication, forming a Rhodic Acrudox having hematite and with strong fine granular structure. Micromorphological analyses showed that both soils contain relict nodules which are probably being dissolved in the current environment, whereas only the Xanthic Acrudox has nodules in current processes of formation due to slower drainage. The Cr horizon of both soils, but mainly the Xanthic Acrudox, presented a much slower saturated hydraulic conductivity than the respective overlying horizons, which was associated with a pattern of poorly connected fissural pores as seen in thin sections. The Cr horizon of the Rhodic Acrudox showed a matrix impregnated by Mn and Fe oxides in an unusual pattern of microlamination and hypocoatings that appear to be unstable, dissolving in the current, strongly drained environment. The soil color is a reliable indicator of such differential pedogenesis in these conditions

Propriedades de solos sob vegetação nativa em Minas Gerais: distribuição por fitofisionomia, hidrografia e variabilidade espacial

A distribuição das formações vegetais nativas depende dos fatores de formação do solo, entre outros aspectos. Dessa forma, solos sob vegetação nativa podem informar muito sobre uma região e sua fertilidade natural, constituindo um testemunho das condições encontradas antes da ocupação agrossilvopastoril. O objetivo deste estudo foi avaliar propriedades químicas e textura dos solos sob fragmentos de Cerrado e florestas nativas amostrados durante o Inventário Florestal de Minas Gerais, por meio de análises de fertilidade do solo, textura e estatística espacial. Em geral, houve grande variabilidade em todas as propriedades analisadas, exceto em Al trocável. Os solos sob Campo Cerrado apresentaram maiores teores de matéria orgânica, comparados aos sob Cerradão e Cerrado stricto sensu. As Florestas Estacionais ocorreram, em geral, em solos de melhor fertilidade natural do que aqueles sob Cerrado, enquanto as florestas sob clima chuvoso ocorreram nos solos mais ácidos e com maiores teores de matéria orgânica, entre todas as fitofisionomias. Análises de regressão linear indicaram que a importância da matéria orgânica na CTC a pH 7,0 variou entre as diferentes fitofisionomias, sendo não significativa para as Florestas Deciduais. A estratificação por bacias hidrográficas, interpretada em conjunto com a fitofisionomia, permitiu também concluir sobre um provável efeito dos materiais de origem nas propriedades do solo, especialmente a textura. Por meio de análise geoestatística, foi possível construir, por krigagem ordinária, mapas do Estado com a distribuição de teores de carbono orgânico do solo, argila e pH, mas não para CTC a pH 7,0. A análise de solos sob fragmentos de vegetação nativa oferece potencial para uso como referência do padrão de fertilidade natural dos solos e é uma iniciativa que poderia ser empreendida em outras unidades da federação