AN IMPROVED CAPACITANCE SENSOR FOR IN-SITU MONITORING OF SOIL-MOISTURE

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 a spects: the measured matrix is contained within the sensor; and the ai r space between the soil and the probe, which adds an undesirable back ground, is reduced. Soil moisture changes, not dependent on salinity, correlated well with both water matric potential and water content det ermined gravimetrically. An SMS installed at 0.45 m depth produced a v oltage drop of similar to 15 mV for each mm of applied irrigation wate r. The SMS is suitable for controlling irrigation, detecting leaks fro m disposal containers, fuel tanks, or water reservoirs, and monitoring liquid level.