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    ABSTRACT: Experimental shifting cultivation was carried out at two sites, Niah and Bakam in Sarawak, Malaysia. The plots (10 × 10 m2) were treated with burning of vegetation biomass (fuel), amounting to 100, 200 and 300 Mg ha−1 with an untreated control at the Niah site and 20 and 100 Mg ha−1 with an untreated control at the Bakam site. At the Niah site, the soils were acidic with a light clay texture. The levels of pH, exchangeable bases and available P of the soils at the depth of 0–5 cm increased by burning while those of exchangeable Al and Al saturation decreased. The changes tended to be more appreciable in the plot treated with fuel at the rate of 300 Mg ha−1 than in the other plots. Based on a comparison between ash alkalinity and the difference in the content of exchangeable Al at 100 d after burning and before burning, it was assumed that 60% of the alkalinity contained in ash was consumed for inactivating exchangeable Al at the depth of 0–5 cm, which resulted in minimal changes in the soil properties in the deeper layers. The influences of burning persisted at the depth of 0–5 cm in all the burned plots until 1 year after burning, except for exchangeable K and available P. On the other hand, at the Bakam site, the soils showed an acidic nature with a sandy loam to sandy clay loam texture. The changes in the pH values and levels of exchangeable bases and Al were observed only at the depth of 0–5 cm in the plots treated with fuel at the rate of 100 Mg ha−1. During rice cultivation, these values returned to the levels recorded before burning. Comparison of the amounts of nutrients among soils, ash and runoff water during rice cultivation at the two sites showed that 1) the losses of ash nutrients by runoff water, except for N, were negligible compared with the amounts contained in the soils and ash, 2) the N input from ash and output by runoff water were not significant, compared with the large stock in the soils, and 3) the ash addition significantly contributed to the supply of inorganic bases (Ca, Mg, K and Na) and P.
    Soil Science and Plant Nutrition 08/2005; 51:525-533. · 0.89 Impact Factor
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    ABSTRACT: Uncertainties in the rate of biomass variation with forest ageing in tropical secondary forests, particularly in belowground components, limit the accuracy of carbon pool estimates in tropical regions. We monitored changes in above- and belowground biomass, leaf area index (LAI), and biomass allocation to the leaf component to determine the variation in carbon accumulation rate with forest age after shifting cultivation in Sarawak, Malaysia. Nine plots in a 4-year-old forest and fourteen plots in a 10-year-old forest were monitored for 5 and 7 years, respectively. Forest and plant part biomass were calculated from an allometric equation obtained from the same forest stands. Both above- and belowground biomass increased rapidly during the initial decade after abandonment. In contrast, a much slower rate of biomass accumulation was observed after the initial decade. LAI also increased by approximately double from the 4-year-old to 10-year-old forest, and then gently increased to the 17-year-old forest. We also found that allocation variation in leaf biomass and nitrogen was closely related to the rate of biomass accumulation as a forest aged. During the first decade after abandonment, a high biomass and nitrogen allocation to the leaf component may have allowed for a high rate of biomass accumulation. However, reduction in those allocations to leaf component after the initial decade may have helped to suppress the biomass accumulation rate in older secondary forests. Roots accounted for 14.0–16.1% of total biomass in the 4–17-year-old abandoned secondary forests. We also verified the model predicted values for belowground biomass by Cairns et al. (1997) and Mokany et al. (2006), although both models overestimated the values throughout our data sets by 45–50% in the 10-year-old forest. The low root:shoot ratio in the secondary forests may have caused this overestimation. Therefore, our results suggest that we should modify the models to estimate belowground biomass considering the low root:shoot ratio in tropical secondary forests.
    Forest Ecology and Management 01/2010; 260(5):875-882. · 2.77 Impact Factor
  • Tropics 01/2009; 18(3):115-126.

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