Spatiotemporal Variability in Soil Water Content Profiles under Young and Mature Oil Palm Plantations in North Bengkulu Regency

Abstract

Soil water content (SWC) profile refers to the vertical distribution of volumetric SWC at a certain depth of soil concerning the plant water availability. The current study aimed to evaluate the vertically spatial distributions and temporal variations in SWC profiles under young and mature oil palm trees during the end period of the rainy season. Twenty couples of sensors were inserted into 5 cm soil depth intervals up to 100 cm. Each sensor pair was connected to the dielectric instrument to measure the electrical impedance (Z, in kΩ) at each soil layer. The measured Z was then converted to the gravimetric SWC (θg, in g.g-1) using an equation of θg = 0.62.Z-0.2 found in our previous study. The gravimetric SWC data were then multiplied by soil bulk density for corresponding layers to get volumetric SWC (θv, in cm3.cm-3). Results showed that soil water profiles' depths were 40 to 70 mm higher under mature than under young oil palm plantations during six weeks of measurements. The vertical distribution of soil bulk density could be why the spatiotemporal variability in water content profile. Looser layers throughout the young oil palm soil profile might cause a higher proportion of drainage pores and result in less water content compared to the denser layers under the mature oil palm.