Soil water movement behavior under oil palm tree of different ages
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Date
2019
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Publisher
Universiti Teknologi Malaysia
Abstract
The expansion of areas planted with oil palm has raised concern over the impacts of related activities on the hydrological processes. One obvious gap is on the knowledge of infiltration and soil water movement processes. The overall objective of this study is to investigate the pattern of water movement in soil and how this pattern is influenced by rainfall intensity and soil properties. Infiltration and soil water movement underneath stemflow and throughfall areas of 9, 15 and 21 years old oil palm trees were investigated. Infiltration was measured at the underneath and interspace of oil palm trees at three successive tensions of -5, -2 and 0 cm H2O using tension disc infiltrometer. Rainwater infiltration and distribution processes were determined by measuring soil moisture content for three different events (before, during and after rain) using aqua Davinci soil moisture probe at the depths between 15.2 cm and 91.4 cm. HYDRUS-1D software that uses van Genuchten (vG) model was then applied to estimate the soil hydraulic properties and to simulate the soil water movement under the three different events. The result showed that the soil bulk density decreased with increasing age of oil palm tree, but vice versa for total porosity. Soil organic matter content and saturated hydraulic conductivity decreased with increasing soil depth for both under stemflow and throughfall areas. The ranges of available water content (AWC) from all study sites were between 20.0% to 31.0% which were acceptable for sandy loam and sandy clay loam soils. The soil water retention curves and hydraulic conductivities obtained by numerical inversion method were in agreement with the measured values and those derived using Wooding’s solution. The soil moisture content at various depths under stemflow and throughfall areas are 34.4% just after rain events, 34.0% during rain events and 31.6% before rain events. The observed soil moisture content decreased with increasing soil depth at all sites for both stemflow and throughfall areas. However, the simulated soil moisture content by HYDRUS-1D software showed no respond to rainfall sizes at the depth more than 30.0 cm. It is evident that the soil bulk density, total porosity, soil texture, intensity and duration of rainfall influenced the infiltration mechanism and water movement in unsaturated soil.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Groundwater flow, Soil moisture, Soil infiltration rate—Measurement