DEVELOPMENT OF TENSIOMETER TO MEASURE WATER POTENTIAL IN THE SOIL

Abstract

The tensiometer is widely used in irrigation study and research as an indicator to note the water potential of the soil. Tensiometers are especially useful in recording water potential at remote field location. An electronic tensiometer with a microcontroller based data logging system was designed and calibrated to provide a portable tensiometer for determining soil water potential. The device consists of a strain gauge arranged in wheatstone bridge form, a porous ceramic cup, a differential amplifier circuit and a data logging system for amplifying, digitizing and acquiring data. Data from the data logging system can be downloaded in a personal computer by removing the microSD card onboard the microcontroller and the computer can download the data on the microSD through the microSD card reader. In calibrating the instrument a standard bourdon gauge is used to measure the pressure exerted on the strain gauge and the corresponding voltage displayed on the multimeter was recorded along with the pressure displayed by the bourdon gauge. In evaluating the instrument, ten readings of data displayed by the developed tensiometer were compared with a Decagon T5 tensiometer readings, resulting in a correlation coefficient of 0.986. The tensiometer performance was reliable, the mechanical and electrical parts worked without malfunctioning. The device is very light, easy to use and more economical compared to those purchased from foreign countries.