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Title: Effects of Acacia mangium on soils in Sabah
Author: Majalap, Noreen
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1999
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Soil changes occurring under A. mangium were studied by comparing soil chemical properties between A. mangium plantations and adjacent non- A. mangium areas, both on a regional and a local scale. Soil pH, exchangeable base cations (especially Ca), and base saturation decreased under A. mangium while exchangeable acidity and Al increased. Translocation of base cations down the soil profile was shown by a decrease in their concentrations in the upper parts of the soil profile and an increase at depths. This appears to be related to an increase in organic C and N content in the lower soil horizons. Solute chemistry and fluxes in precipitation, throughfall, stemflow and in the forest floor, at 30 and 60 cm soil depth were studied. Rates of litter production, litter decomposition and N-mineralization were also quantified. Canopy interception of precipitation was high (20%) resulting in retention of most of the solutes. These, however, were later released in considerable amounts from the forest floor. Dissolved organic C showed the highest flux from the forest floor. Litter production was high under A. mangium at 12 t ha-1 yr-1 while leaf litter decomposition rate was relatively low at 0.45 yr-1 suggesting that forest floor as a significant source of organic acids. While considerable NO3-N flux from the forest floor was also seen, concentration of NO3-N was highest in the surface mineral soil. Soil nitrification rate was estimated as 17.7 g g-1 30 d-1 for the 0-15 cm depth. In a laboratory soil leaching experiment, interactions of throughfall and stemflow solutions with A. mangium litter caused significant changes in the soil chemical properties. Retention of DOC in the soil plus the continual increase in leachate pH suggest enhanced weathering. Increase in soil pH, exchangeable bases and base saturation was observed suggesting that in the short term A. mangium results in 'ameliorative' effects on the soils, but may be deleterious in the long-term especially on highly weathered soils.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available