Soil water determination by natural gamma radiation attenuation

Abstract

The purpose of the study was to determine the soil moisture content by measuring the naturally occurring gamma radiation in the soil. A calibration procedure was developed both in laboratory and in the field. In the laboratory, two different sample sizes were used: three-inch diameter, and 18-inch diameter columns, both 15 cm long. Small size soil samples (three-inch diameter) cannot be used to predict the calibration curve in the field, whereas the larger soil samples (18-inch diameter) calibration may be used to predict the field calibration curve. The prediction limits for the calibration curve done in the field are of ±5%, which is an unacceptable level of precision. It was also observed that the distance between the detector and the soil should always be kept constant, and that the top 15 cm of the soil contribute to approximately 95% of the radiation measured at the soil surface.