Laboratory accuracy of soil moisture sensor irrigation controllers

Bernard Cardenas-Lailhacar, Michael D. Dukes


It has been demonstrated that soil moisture sensor systems (SMSs) can reduce irrigation application in Florida. However, SMSs have not been tested under Florida soils irrigated with reclaimed water, which contains salts that can affect the measured soil water content. The objective of this research was to test different commercially available SMSs under controlled conditions, and analyze their responses and readings under different levels of water salinity and temperature. Three brands/models were selected for this experiment: Acclima/SCX, Baseline/WaterTec S100, and Dynamax/IL200-MC. Different design methods were pretested. The selected method consisted of containers manufactured so that they could be saturated from the bottom to minimize entrapped air and fitted with sintered metal filters to allow vacuum application for water removal in a timely manner. The containers were installed in a controlled-temperature chamber so that they could be saturated and dried down across three temperatures (5, 25, and 35 °C). The water applied will have an electrical conductivity of 0.0, 0.7, and 5.0 dS·m–1. Each container was placed on a platform-scale to determine soil-water loses, by weight variation over time. The scale readings are compared to the SMS readings, and a calibration curve is developed through regression analysis. Preliminary outcomes show that most treatments resulted in linear regressions with R2 values higher than 0.92, corroborating that this laboratory design is adequate for verifying the precision and accuracy of the SMSs tested over a range of salinity values, water contents, and temperatures.

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283