An Improved capacitance sensor for in situ monitoring of soil moisture

Abstract

A low-power, capacitance-based penetrating soil moisture sensor (SMS) is presented. The SMS is battery-operated, inexpensive, and simple to use. The sensor differs from previous capacitance-based devices in 2 aspects: the measured matrix is contained within the sensor; and the air space between the soil and the probe, which adds an undesirable background, is reduced. Soil moisture changes, not dependent on salinity, correlated well with both water matric potential and water content determined gravimetrically. An SMS installed at 0.45 m depth produced a voltage drop of ~15 mV for each mm of applied irrigation water. The SMS is suitable for controlling irrigation, detecting leaks from disposal containers, fuel tanks, or water reservoirs, and monitoring liquid level.