Effect of Para Rubber Tree Planting on Some Soil Hydrological Properties in Eastern Coast Subwatershed, Rayong Province

Abstract

Land use change, especially an increasing area under para rubber, has affected soil hydrology related with soil infiltration and soil water storage which influence the water yield in a watershed. The objectives of this research were to study the effect of para rubber plantation on some soil hydrological properties at the Eastern Coast subwatershed, during both wet and dry period in 2017. Soil samples were collected using undisturbed technique for determination of soil moisture content, soil bulk density, and soil hydraulic conductivity, while soil infiltration was done by a single ring infiltrometer. F-test was used for statistical testing. The results indicate that the soil texture in the area under para rubber plantation was sandy loam with low soil organic matter. Average soil moisture content during the dry period in the topsoil and subsoil was 7.66% and 9.21%, respectively, while during the wet period, it was 16.62% and 14.17%, which was similar to a natural forest in the study area. Besides, soil moisture increased during the wet period due to rainfall. The soil bulk density during the dry period in the topsoil and subsoil was 1.43 and 1.56 g cm^-3, respectively, which was similar to the levels in the natural forest, but soil bulk density at subsoil in para rubber area was greater. The soil infiltration rate (f_c) in the para rubber area was 153.44 mm h^-1 and 119.99
mm h^-1 during the dry and wet periods, which indicated to a lower soil infiltration capacity compared to the natural forest but higher than in a fruit orchard in the study area. It can be concluded that the para rubber tree plantation in the Eastern Coast subwatershed has some effect on the soil bulk density, particularly at the subsoil level and that in the younger para rubber tree planting area showed a reduced soil infiltration capacity than in the area with older trees.