White, P.A. 1994 The use of resistivity methods to measure soil moisture levels. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 94/05 iii, 34 p.
Abstract: Resistivities measured at approximately weekly intervals for a year at an experimental site at Eyrewell, North Canterbury, showed an inverse relation to soil moisture. Resistivity declines steeply for increasing soil moisture in the range 5-10%, but is less dependent on changes in soil moisture when the soil moisture content is above 10%. The resistivity method appears to be sensitive enough to detect soil moisture conditions that cause plant wilting. The relationship between measured resistivity and soil moisture is described by existing equations which calculate correlation coefficients in the range -0.846 to -0.895. Variations of resistivity in layers within the top few centimetres of ground can be detected by the Wenner sounding method. Derived layer resistivity values are not as well correlated to neutron meter moisture changes as are directly-measured resistivity values. The Wenner sounding method has been shown to be capable of measuring changes in soil moisture in the depth range 0-16 cm, which is shallower than the recommended depth range of nuclear moisture meters. (auth)