NONINVASIVE SOIL-WATER CONTENT MEASUREMENT USING ELECTROMAGNETIC INDUCTION

The feasibility of soil water content measurement using electromagnetic induction was investigated in an arid region of southern New Mexico. Soil water measurements were taken monthly with a neutron probe at 65 equally spaced stations along a 1950-m transect. At the same time, noninvasive electrical conductivity measurements of the soil were taken with a Geonics EM-31 ground conductivity meter. Using 16 months of measurements, we found a linear relationship exists between bulk soil electrical conductivity and total soil water content in the top 1.5 m of the profile. A simple linear regression model was developed to describe the relationship between soil water content and bulk soil electrical conductivity. The spatial and temporal accuracy of the regression model is addressed as well as the total number of neutron access tubes needed to accurately calibrate the model. By comparison with the neutron scattering method the electromagnetic induction method is quite accurate for the prediction of water content changes over time. The speed and ease of use combined with the accuracy of the measurements make the ground conductivity meter a valuable tool for rapid, noninvasive soil water measurements.