In-situ measurement of soil evaporation from a volcanic ash soil by TDR technique using soil water diffusivity

The investigation was undertaken with a view to qualifying the time domain reflectrometry (TDR) technique for prediction of evaporation from a volcanic ash soil in the experimental plot of National Institute of Agro-Environmental Sciences (NIAES), Tsukuba, Japan. The inputs for prediction involved automated measurement by TDR of soil water content in-situ and a flow property called ‘soil water diffusivity’, D(θ), estimated from TDR-measured soil water content data depthwise from a drying soil column. Results suggest that TDR water content data obtained from field repetitively at different depths over a period of 48 days could reasonably predict evaporation from 3.5-cm soil depth using TDR-derived D(θ) values from a drying soil column. However, the capability of the TDR technique in predicting soil evaporation depends so much on the use of calibrated values of TDR soil water data to the original Toppʹs equation. The daily averages for predicted evaporation were 1.06, 0.90 and 0.96 mm for the months of December, January and February, respectively.