Dr. Daran Rudnick
Date of this Version
J. Singh, Performance Assessment of Electromagnetic Soil Water Sensors in Different Soil Textural, Temperature, and Salinity, M.S. thesis, University of Nebraska-Lincoln, 2017
Determination of accurate and continuous measurements of volumetric water content (θv) is extremely valuable for irrigation management and other agronomic decisions. Lately, electromagnetic (EM) sensors are being widely used to monitor θv continuously which also offer the benefits of ease of installation, fewer regulatory and safety concerns, and cost effectiveness. However, the accuracy of parameters [soil temperature, electrical conductivity (ECa), dielectric permittivity (εra), and θv] reported by EM sensors need to be evaluated for them to be utilized for agricultural water management. In the current study, the accuracy of a wide range of EM sensors was evaluated over field and laboratory conditions. The performance of eight EM sensors (TDR315, CS655, HydraProbe2, 5TE, EC5, CS616, Field Connect, AquaCheck), was analyzed through a field study in a loam soil. In addition, performance assessment of two improved and recently developed EM sensors (TDR315 and CS655) was done in a laboratory over different soil type, temperature, and salinity conditions. For the field study, the reported temperature and ECa difference among the sensors were within 1°C and 1 dS m-1, respectively. Among the single-sensor probes, the range of depth-combined (0.15 and 0.76 m) RMSD for factory calibration varied from 0.039 m3 m-3 (5TE) to 0.157 m3 m-3 (CS616). Regression calibrations improved θv accuracy substantially beyond factory calibrations and the betterment in θv accuracy gained by using offset calibrations was smaller and less consistent than the improvements gained by using regression calibrations. For the laboratory study, the models for estimation of θv at hot (35°C) and cold (23.9°C) temperature were not significantly different from each other (two-tail p-value within 0.1387 and 0.7231) for TDR315 and CS655 sensors. The models for no salinity and added salinity were significantly different from each other (two-tail p-value within 2.2 × 10-16 and 0.005). It was found that CS655 and TDR315 calibration varied with soil type and the relationship of the calculated coefficients (quadratic, linear, and intercept) for CS655 and TDR315 sensors across each soil type were investigated with respect to their clay content. Based on external validation of the relationships of TDR315 and CS655 sensors with the clay content, it was found that soil type has a noteworthy effect on the performance of CS655, but not TDR315 sensors. Future work aiming to test the developed universal calibration would strengthen the claims of this study and may signal new opportunities.
Advisor: Daran Rudnick