The Effect of Soil Salinity on Accuracy of Soil Moisture Sensors

【Objective】 Soil moisture sensors have been increasingly used in different fields to measure soil water content at high temporal resolution, but its reliability depends on many factors. In this paper, we investigate the effect of soil salinity on their accuracy. 【Method】 The laboratory experiment was conducted at the Irrigation Test Station of the First Division of Xinjiang Alaer Corps. FDR and TDR sensors were used in the experiment. We compared five salinity treatments: 2, 3, 5, 7, 9 mS/cm; the soil moisture was adjusted to the field capacity followed by natural evaporation. The absolute error (AE), relative error (RE) and standard deviation (SD) were used to evaluate the accuracy and consistency of the sensors. 【Result】 Soil moisture and salinity both affected accuracy and consistency of the sensors. Without calibration, the accuracy of the CSF11 and ML2x sensors was high and measurements were consistent, while the EC-5 and TDR305H sensors were less accurate and consistent due to the combined influence of soil salinity and moisture. Calibration significantly improved the accuracy and consistence of all four sensors. 【Conclusion】 Considering accuracy and consistency, the expensive ML2x sensors worked best when salt content does not exceed 9 mS/cm. The less expensive CSF11 sensors also worked well when soil salt is low. The EC-5 sensors can measure soil moisture reasonably well for soil with moderate and high salinity. When the soil moisture is less than 20 cm3/cm3, TDR305H sensors is accurate and reliable.