Pore size distribution of soils in the tropical rain forest and the rubber plantation in Southern Thailand
1989
Samakkee Boonyawat | Chaiwat Kongsom (Kasetsart Univ., Bangkok (Thailand). Faculty of Forestry. Dept. of Conservation)
Pore size distributions were different. The quantity of large pore-size (8.6-28.4 micrometer) of top soil in the tropical rain forest and in the rubber plantation was 26.20 and 17.96 % and in the sub soil were 24.81 and 18.37 %, while the quantity of small pore-size (0.2-8.6 micromrter) of the top soil were 6.06 and 8.57 % and in the sub soil were 4.05 and 8.26 % respectively. Moreover the change of tropical rain forest to be rubber plantation caused the decreasing of the total porosities of soil about 2.49 % in the top soil and about 0.36 % in the sub soil. According to the variation of various size of pore-size distribution, it caused the decreasing of pore-size quantity that effected to water storage and drainage, for the large pore-size in the top soil and in the sub soil about 8.24 and 6.44 % respectively. In case of small pore-size, percentage of water storage and drainage capability of the top soil was increased 2.51 % but in the sub soil was decreased 4.21 %. This result effected to the decreasing of soil capability (the drainage capability were confirmed by saturated hydraulic conductivity that would be decreased from 131.87 x 10-4 cm/second to 76.19 x 10-4 cm/second in top soil and from 121.95 x 10-4 cm/second to 71.52 x 10-4 cm/second in sub soil.). Therefore, it could be said that, the change of the tropical rain forest to the rubber plantation area caused the change of pore-size distribution and other physical properties of soil that affected to the degradation of hydrological properties, which caused flood more hazardous.
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