Design, Development and Evaluation of a Continuous Capacitance-based Sensor for On-the-Go Soil Moisture Content Measurement

Soil compaction and moisture content are two of the factors that greatly influence variations in crop yield. Capacitance-based sensor is a sensitive device for estimating soil water content. In this method of soil moisture content measurement, soil acts as the dielectric of the capacitor. Throughout this research work, a capacitance-based moisture sensor that can measure the soil moisture content in a continuous manner, was developed and tested. The developed moisture sensor consisted of two parts namely: three electrodes and an electronic circuit. The electrodes are heat treated metallic terminals which with the needed heat treatment have became tough and their surfaces abrasion-resistant. These terminals are embedded in pieces of fiberglass. The excitation voltage of the electronic circuit was 12V with its output response being the frequency factor. The sensor was tested under static laboratory conditions, employing a silt clay loam type soil. The developed sensor was evaluated in filed conditions. An analysis of the results showed that the relationship between the soil water content and the output frequency could be presented through a quadratic. The error of the sensor was estimated as 1.55%. There was a significant correlation (R2=0.70) between the soil water content measured through the sensor, and that estimated through the gravimetric method. The results indicated that, the sensor output data, in addition to being influenced by soil moisture content, they were also affected by soil temperature.