Modeling Soil Complex Dielectric Permittivity via Frequency Domain Analysis of Time Domain reflectometry (TDR) waveforms.
Xiufu Shuai, N-122H Ag Sci North, University of Kentucky-Dept. of Pla, University of Kentucky, Dept. of Plant & Soil Sciences, Lexington, KY 40546, Riley Walton, University of Kentucky-Dept. of Plant and Soil Science, N-122H Ag Sci North, Lexington, KY 40546, and Ole Wendroth, University of Kentucky-Dept. of Plant and Soil Sciences, N-122M Ag Sci North, Lexington, KY 40546.
Time domain reflectometry (TDR) is widely used to simultaneously measure soil water content and electrical conductivity (EC) of soils. However, it fails to measure water content at high salinity. Mechanical model of soil dielectric permittivity combined with calibrated transmission lines can be used to solve the problem. In the four component mixing model, four components, i.e. free water, bound water, air and solid, are considered. The objective of this study is to test this model and estimate the water contents and bulk EC using frequency domain analysis of TDR waveforms of silt-loam soil columns with different levels of water contents and EC. Results show that the linear four-component mixing model can be used; the estimated bound water content is 0.12 m3 m-3; the soil volumetric water contents can be estimated even at high salinity condition; and the estimates of EC are very close to the measured ones.