A liner offset equation of the volumetric water content that capacitance type GS3 soil moisture sensor measured
2015
Mitsuishi, S. | Mizoguchi, M.
The ECH2O GS3 soil moisture sensor (GS3, Decagon Devices, Inc.,) is suitable for measuring volumetric water content (theta), temperature, and bulk EC for agricultural materials. Two types of calibration equations are provided for the GS3 water content measurements: a standard equation (theta sub(ST)) and an agricultural material equation (theta sub(AM)). In this study, these two equations were evaluated based on the dry weight method theta (theta sub(M)) for agricultural materials (Rock wool, Vermiculite, Peat moss, and Strawberry soil) and soils (Toyoura sand, Andisol and Kanto loam). The relative error of theta sub(ST) was 10 % - 14 % for agricultural materials, 3 % for the sand, and 14 % for the Andisol and Kanto loam. The theta sub(ST) prediction was reasonably accurate for Toyoura sand, but practically not applicable for agricultural materials, Andisol, and Kanto loam. The relative error of theta sub(AM) was 8 % - 10 %. The accuracy of theta sub(AM) was slightly higher than for theta sub(ST) regardless of samples. The theta sub(ST) was corrected based on the linear regression line for the theta sub(M) and theta sub(ST) relationship. The relative error for the corrected theta sub(ST) became 1 % - 5 % for all samples. Furthermore, the linear regression line was made according to three saturated, intermediate, and dried samples (3-point method). The relative error for the theta sub(ST) corrected with the 3-point method was 2 % - 6 %, which was much smaller than for the original theta sub(ST). In conclusion, we recommend using the 3-point method to correct theta sub(ST) for the GS2 measurements for soils snf agricultural materials.
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