Estimation of Soil Water Content Using a 50 MHz Impedance Sensor: Soil Texture, Structure, and Salinity Interactions

摘要

The Hydra Probe (HP) measures soil volumetric water content ( ? _v ) with an electrical impedance sensor that operates at a frequency of 50 MHz. The main objective of this research was to investigate the mixed effects of texture, disturbance, and salinity on the estimation of ? _v by the HP. Duplicate disturbed and undisturbed samples from three sites with different soil textures (clay, silty clay loam, and sandy loam) were saturated with distilled-deionized water and four saline solutions (corresponding electrical conductivities of 0, 1.23, 2.02, 2.41, and 3.96 dS m -1 ) for three days and then air-dried under laboratory conditions, generating monotonic drying curves. The real ( e _r ) and imaginary ( e _i ) components of the dielectric permittivity were measured every 5 min by the HP and recorded with a datalogger. Load cells simultaneously recorded changing sample weight over time to provide an independent measure of ? _v . Our results indicate that for the range of conductivities in our samples, there is no benefit to predicting ? _v from e _r by also including e _i , or a correction for the loss tangent (i.e., tan d = e _i / e _r ). Regression analysis combined with analysis of variance showed that both soil texture and disturbance significantly influenced the estimation of ? _v from e _r , (p 0.05), while salinity or any of the interactions did not significantly influence its estimation. As quantified by the mean absolute error (MAE), the overall accuracy of the HP in this study was 0.0177 cm 3 cm -3 . Accounting for both soil texture and disturbance reduced the average MAE by 8.45%. Based on these analyses, we recommend that soil texture and disturbance effects be included in the development of future calibration equations for the HP