Evaluation of Gamma Ray Attenuation for Measuring Soil Bulk Density Part II. Field Investigation

A field investigation was conducted at sites near Lexington and Central City, Kentucky, to evaluate the use of gamma ray attenuation for measuring soil bulk density. Experiments were conducted whereby the gamma gauge was calibrated by various means and compared with volumetric cores collected from the field soils. Calibration by the manufacturer’s recommended procedure was determined to be as accurate as more rigorous laboratory calibration or calibration via regression of soil bulk density data, provided that the effect of soil water on gamma attenuation is correctly considered. We also developed a linear regression equation to correct for the occurrence of deviation from prescribed separation distance between the gamma source and detector [254 mm (10 in.)]. Experiments indicated that soil moisture content and soil depth had no effect on the accuracy of determination of dry soil bulk density by the gamma gauge