Enhancing Accuracy in Soil Water Content Measurement: A Modified Dielectric Model Approach

Accurate determination of soil water content through dielectric properties-based methods relies heavily on a dielectric model linking the apparent dielectric constant to the volumetric water content. Recent research highlights the susceptibility of agricultural topsoil porosity to significant alterations, leading to inadequate precision in soil water content measurements. Despite concerted efforts by scientists to enhance dielectric models, challenges persist in ensuring their quality, especially in relation to soil porosity. This paper introduces a modified dielectric model, addressing both soil porosity and residual water content, established through a two-point anchoring calibration using air-dried and saturated soil. The study encompasses extensive theoretical exploration and field investigations examining factors influencing measurement accuracy, such as variations in porosity with water content, compaction effects, air gaps from probe insertions, residual water content, and other parameters in the two-point anchoring calibration. Empirical investigations, conducted in both laboratory and field settings, demonstrate that the modified dielectric model exhibits a maximum absolute measurement error of less than 0.018 m³ m^-3 over a water content range from 0.03 m³ m^-3 to 0.5 m³ m^-3, representative of typical soil conditions in China. The use of air-dried soil and saturated soil for two-point anchoring calibration provides convenience and time efficiency. For the same soil type, in the event of soil disturbance, it is only necessary to substitute the remeasured soil porosity into the established dielectric model. This research contributes to the advancement of precision in agricultural water management, offering applicability in assessing optimal water amounts for efficient plant utilization, soil aeration, and informed irrigation decision-making.