EVALUATION OF A CAPACITANCE SENSOR FOR MONITORING SOIL WATER CONTENT

This paper aims to evaluate a capacitance sensor for monitoring soil water content. Capacitance sensors were tested to evaluate the effect of temperature and response time, and to obtain the calibration equation and their sensitivity. Sensors were placed in different environments (soil, water and air) and temperatures (25 degrees C, 20 degrees C, 15 degrees C, 10 degrees C, 5 degrees C and 0 degrees C). The calibration was performed with one of the capacitance sensors installed in a PVC column containing 0.015066 m(3) of undisturbed soil and hanged on one side of a scale with a load cell connected to a data acquisition board on the other side. Results showed reductions in the frequency response of the capacitance sensor with increasing temperature. The response time was low (less than one second) as it was immersed into water, as well as to an abrupt change in soil moisture in the soil column. It was verified that the sensitivity of the sensor increases as the soil moisture decreases. Therefore, the capacitance sensor can be used to determine the soil moisture.