Effect of Temperature and Salinity on the Precision and Accuracy of Landscape Irrigation Soil Moisture Sensor Systems

It has been demonstrated that soil moisture sensor systems (SMSs) designed for landscape irrigation can save water. However, SMSs have not been tested with reclaimed wastewater. Both salts contained in the irrigation water and temperature might alter the soil water content (SWC) sensed by SMSs. The objective of this research was to quantify the effect of salinity and/or temperature on the precision and accuracy of three different commercially available SMSs. The brands, controllers, and probes selected for this experiment were as follows: Acclima, SCX, and Digital TDT, Baseline, WaterTec S100, and biSensor, and Dynamax, IL200-MC, and SM200. Every SMS was replicated three times. Each SMS probe was installed in the center of different containers filled with an Arredondo fine sand. The containers were placed in a controlled-temperature chamber and were saturated and dried down across a combination of three temperatures (10, 25, or 35°C) and three electrical conductivities (0, 0.7, or 5 dS/m). Each container was placed on a platform scale to determine soil water losses, by weight variation over time. The actual or measured SWCs were then compared with their respective SMS readings. A regression analysis was performed, per brand, for each combination of salinity and temperature. Acclima resulted in the most robust and reliable system, with no practical reading variations when exposed to different combinations of temperatures and salinities. Both Baseline and Dynamax systems were sensitive to high salinity and/or high temperature, making their use more difficult in extreme or changing situations. However, all tested SMSs followed with adequate precision the SWC under the different salinity and temperature scenarios. Consequently, these SMSs might achieve an adequate landscape irrigation control, even when their readings might not correspond to the actual SWC.