CO2-driven cation leaching after tropical forest clearing.

The objective of this study was to investigate the role of dissolved CO2 (H2CO3*) as a mechanism of cation removal from surface soils under secondary land uses in the tropics. Soil leachate columns were prepared with 0?10 cm soils from mature and secondary forest, and managed pastures, and extracted with H2CO3* from deionized water equilibrated with 0%, 0.5%, 1%, and 10% CO2 (g). Extraction of soil cations slowed over time following an exponential form for the cumulative data. The rate of cation concentration decline varied as a function of CO2 concentration with the 10% solution resulting in a greater percent decline with extraction volume. Potassium removal from the exchange sites of all soils and for all solutions was nearly complete ranging from 85% to 97% while removals of Mg (31% to 71%) and Ca (12% to 42%) were lower. The asymptotic patterns of cation loss observed in this study suggest that H2CO3* acid-driven losses of cations may become self-limiting over time. Other stronger acids from atmospheric deposition or organic sources may serve to perpetuate cation removal, and re-forestation on these cleared lands would certainly re-distribute cations from soils to vegetation

Utilização de imagens Landsat e CBERS na avaliação da mudança do uso e cobertura da terra e seus reflexos na qualidade da água em microbacia hidrográfica do município de Paragominas, Pará.

As examples of human activities that may provoke changes in the stability and in the dynamic equilibrium of the river basin system, we have deforestation, burned areas, predatory agriculture, urbanization and other ways of soil occupation without any environmental planning. The combination of remote sensing (TM Landsat and CBERS images ) and geoprocessing products and techniques are valuable tools to subsidize studies of the land use. The results in this first stage of the project indicate a relation between the increasing of the conductivity in the water of microbasin with the increasing of the plantation areas of grains and the decreasing of the primary and secondary forest areas (Capoeiras). The results show that the changes in the use of the land are provoking an increase in the concentration of the nutrients and a consequent diminution of the water quality of the Igarapé Cinqüenta e Quatr

Tree growth soil response to P fertilization in a 24-year-old tropical forest on an Oxisol.

Abstract ID: 82

Dissolved CO2 in small catchment streams of Eastern Amazonia.

Poster 525. Disponível também on-line

The chemistry of two streams draining kaolinitic soils.

Resumo 20.5

Five native tree species and manioc under slash-and-mulch agroforestry in the eastern Amazon of Brazil: plant growth and soil responses.

Throughout the Amazon of Brazil, manioc (Manihot esculenta) is a staple crop produced through slash-and-burn agriculture. Nutrient losses during slash-and-burn can be large and nutrient demand by food crops so great that ?elds are often abandoned after two years. In recent decades, farmers have reduced the fallow phase from 20 to *5 years, limiting plant nutrient accumulation to sustain crop yields. Improved fallows through simultaneous planting of trees with food crops may accelerate nutrient re-accumulation. In addition, slash-and-mulch technology may prevent loss of nutrients due to burning and mulch decomposition may serve as a slow-release source of nutrients. This study in Para´, Brazil, in a 7-year-old secondary forest following slashing and mulching of the vegetation, involved two main plot treatments (with and without P and K fertilizers) and two sub-plot treatments (with or without a N2-?xer Inga edulis). A mixed-culture of trees and manioc was planted in all plots. P and K fertilizer increased tree mortality due to weed competition but growth of surviving trees in four of the ?ve tree species tested also increased as did biomass production of manioc. In the N2-?xer treatment trends of greater growth and survival of four of ?ve tree species and manioc biomass were also observed. Fertilization increased the biomass of competing vegetation, but there was a fertilizer by N2 -?xer interaction as I. edulis caused a reduction in competing biomass in the fertilized treatment. After one year, fertilization increased decomposition of the mulch such that Ca, Mg, and N contents within the mulch all decreased. In contrast, P and K contents of mulch increased in all treatments. No in?uence of the N2 -?xer on 0–10 cm soil N contents was observed. Two years after establishment, this agroforestry system succeeded in growing a manioc crop and leaving a well-maintained tree fallow after the crop harvest

Stream water chemistry assessment in agriculture catchments in Eastern Amazonia.

Poster 568. Disponível também on-line

Throughfall reduction: Impacts on solution nutrient fluxes.

Oral 399. Disponível também on-line