Field Estimation of Soil Dry Bulk Density Using Amplitude Domain Reflectometry Data

Abstract

Since permeability of field soils is strongly affected by dry bulk density, knowledge of spatial distribution of dry bulk density is beneficial to predict water and chemical transport through soils. In this study, field soil dry bulk density was estimated by using Amplitude Domain Reflectometry (ADR) data. The experiment was sited at the Sakae-cho experimental field of Tokyo University of Agriculture and Technology (TUAT) covered by Andisol soil. The field of 4 X4m in large was divided into 81 small plots of 0.5X0.5m each. The ADR probe was operated in every small plot, and the ADR output voltage was measured by using digital voltmeter. Soil samples were taken by using the steel ring of 100 cm3 in volume. The results showed that the estimated dry bulk density agreed well with the measured dry bulk density. The regression coefficient (R2) ranged from 0.4 to 0.7. Dry bulk density estimated by using the ADR data and wet bulk density (R2=0.5-0.7) had greater accuracy than that by using the ADR data and mass wetness (R2=0.4-0.6). Furthermore, spatial variability, which was expressed by semivariogram, of the measured and the estimated dry bulk density by using the ADR data and wet bulk density agreed well. However, spatial variability of the dry bulk density estimated by using the ADR data and mass wetness showed different trend to others. This indicated that the estimated dry bulk density with wet bulk density had better performance to predict dry bulk density than that with mass wetness.