FABRICATION AND CALIBRATION OF LOW COST CAPACITIVE SOIL HUMIDITY SENSOR

Abstract

Soil humidity is critical in crop production and its control is essential to water conservation. The knowledge of soil humidity to majority of farmers in Kenya is based on effects of weather on crops and soil texture. Projected population increase leads to requirement of food in large quantities which is a challenge to sustain on rain fed agriculture .The country will be compelled to practice irrigated agriculture to satisfy the demand of food by its population. Research has shown that high yield is realized when irrigation is done with an aid of soil moisture census such that, water applied to crops is done at the right time and amount applied is just enough for their hydric needs at various stages of crop growth and development. This derives the need to develop soil humidity sensor that can give continuous signal reflecting amount of water in the soil. The research focused on fabrication of a capacitive soil humidity sensor using cheap locally available materials and calibration of the sensor using oven dry method in which capacitance of the soil, was measured with corresponding gravimetric soil water content. Results shows that the relationship between capacitance (C) of the soil and gravimetric soil water content Өg is polynomial equation of third degree with strong correlation coefficient R2 ranging from 0.95249 to 0.9877 for four soil texture classes calibrated. Therefore calibrated capacitance can be used for real-time estimation of gravimetric water content.