Design and Field Evaluation of a New Controller for Soil-Water Based Irrigation

A new irrigation controller was developed using readily available components and coupled with an inexpensive dielectric soil water probe. The electronic controller was designed to be easily adapted to existing commercial irrigation systems that currently use time clocks with a pressurized water supply. The total cost of components used in this controller (not including shipping or labor costs) was US$124 including the US$60 sensor. The new device was field tested against other common automatic scheduling methods (fixed timer and variable timer based on historical evapotranspiration) on a drip-irrigated plastic-mulched tomato field in South Florida. The soil water feedback irrigation control with this new device saved up to 74% water while maintaining yields with respect to the typical fixed irrigation schedule rates applied by commercial tomato growers during the winter season in the area. Comparisons with evapotranspiration-based application rates for the area also showed water savings of up to 61%. Although similar savings (up to 79%) were obtained with switching tensiometers, in the gravelly soils of the area these devices are difficult to maintain requiring refilling at least twice a week whereas the soil-water controller required no maintenance throughout the season. The new controller proved reliable and simple to use. It is recommended that the irrigation set-point be validated in the field at the beginning of the season. The study shows that the combined variability of the soil and the water probes resulted in relatively high variability of water application, although the resulting variability in the yield response was less.