Testing of a Field Dielectric Soil Moisture Meter

Abstract

Abstract The functional relationship between dielectric constant and soil content has been applied to the development of a dielectric soil water moisture meter based on converter capacitance-frequency. A measured capacitance forms part of the tuning capacitance of an oscillator and causes a definite frequency deviation. A cylindrical probe fitted with an oscillator is used to measure the electrical field. The author has determined the basic characteristics of the instrument—center of sensitivity, radius of the electrical field, and influence of soil properties, particularly changes in bulk density, chemical composition, and temperature. The device is applicable for either continuous use, with the probe permanently built in to the soil layer, or use with the probe sliding inside an access tube, in which case the vertical distribution of soil moisture is measured. Field calibration of the meter is required.