Measurement of soil moisture change in spatially heterogeneous weathered soils using a capacitance probe

A capacitance probe has been employed to measure the spatial and temporal change of soil moisture in a weathered soil profile with heterogeneous texture characteristics. Measurements were made to a depth of 2 m at intervals of 2 cm. The field work was carried out during a wetting-up period in a subtropical monsoonal environment in the Middle Hills of Nepal. Calibrations of the frequency readings against gravimetric and volumetric soil moisture are compared. It was found that the frequency reading correlates much better with the volumetric soil moisture. Although the soil is spatially heterogeneous in its particle size, porosity and bulk density, it was found that a single regression equation can be used to represent the relationship between the frequency reading of the capacitance probe and volumetric soil moisture. The results demonstrate that the capacitance probe enables the investigation of soil moisture variation temporally and spatially at high resolution and can measure a wide moisture range. (C) 1998 John Wiley Sons, Ltd.