Abstract
It is worthy to know the distribution of soil physical properties in the field to gain better understanding of soil behavior. However, taking undisturbed core samples in situ is usually laborious and time consuming. In this study, estimation of dry bulk density of soil by using Amplitude Domain Reflectometry (ADR) data was conducted. The dry bulk density can be calculated by combining volumetric water content measured by using the ADR probe {θADR} with either wet bulk density or mass wetness. Andisol (TUAT soil) and Alluvial soil (Fukaya soil, Saitama) was used in this study. Soils were sieved through 3 mm mesh screen, and packed into a plastic acrylic cylinder of 68 mm in inner diameter and 69 mm long. Mass wetness ranged from 40-70% and 15-30%, and packing dry bulk density ranged from 0.39-0.96gem-3 and 0.78-1.30gem-3, for the TUAT and the Fukaya soil, respectively. Three replicated ADR readings of output voltage were measured by using a digital multimeter. The θADR was calculated by using a calibrated polynomial equation, as a function of the averaged output voltage. The results showed that the output voltage was not affected by neither packing dry bulk density nor mass wetness. The estimation of dry bulk density with wet bulk density (R2 value=0.989-0.994, RMSE value=0.010-0.014gem-3) was better than that with mass wetness (R2 value = 0.913-0.961, RMSE value=0.027-0.038gem-3). The accuracy of the θADR was a critical factor in estimating dry bulk density.
