Accuracy of Handheld and Buried Moisture Sensors in a Saline Soil.

Soil moisture sensors are increasingly being used by turf managers to accurately determine irrigation requirements. However, the use of saline water and subsequent increase in soil salinity can affect moisture measurements of time or frequency domain sensors. A laboratory study was conducted at New Mexico State University to test the accuracy of 4 moisture sensors in a range of soil salinities. Sensors included in the study were TDR300 (Spectrum Technologies Inc.), POGO (Stevens Waters), Turfguard (The Toro Company) and 5TE (Decagon). Sand meeting USGA specifications for particle size distribution was used for the study. Sodium chloride was added to tap water to reach salinity concentrations, of 2, 4, 6, 8, 10, 15, 20, 40 dS m^-1. Tap water (0.5 dS m^-1) and distilled water (0 dS m^-1) were included as control treatments. Container measuring 10 cm in diameter and 10 cm in height were filled with sand and irrigated with water in varying amounts and salinity levels. Soil salinity was determined on the saturated paste extract. Soil moisture was determined both gravimetrically and through instrument readings. The TDR300 measured accurately to salinity level of 0.5 dS m^-1, however, as salinity increased moisture readings were higher than measured values but deviated linearly. This indicated that with correct calibration, the TDR300 can report moisture content accurately even at high salinity. The POGO and the 5TE sensors performed well to salinity levels as high as 15 dS m^-1. The Turfguard sensor was the least affected by salinity, maintaining an accurate range of readings with salinity as high as 40 dS m^-1. More research is necessary to investigate the effects of different soil types or a turf canopy.