Texture and electrical conductivity effects on temperature dependency in time domain reflectometry

If not accounted for, temperature effects on the water content and electrical conductivity measured with time domain reflectometry (TDR) will introduce significant errors. In this study, an automated TDR system was used to quantify the temperature dependence of the apparent dielectric constant and electrical conductivity in wet soils. Sandy, clayey, and organic soils were used to examine the effect of soil texture. The temperature correction factor for water content measurements was predicted, by using different dielectric mixing models, to lie between -0.00253 and -0.00419 theta degrees C-1, the negative value of the temperature correction factor indicating a decrease in the water content measurements with increasing temperature. These values agreed wed with the correction factor measured in sandy soils: -0.00269 theta degrees C-1. In soils with large specific surface, i,e,, clayey and organic soils, however, the temperature dependence was significantly lower, Large specific surface combined with high soil solution electrical conductivity resulted in a positive correction factor, i.e,, water content measurements increased with increases in temperature, The temperature dependence of the bulk electrical conductivity was investigated using different soils and soil solutions. The temperature dependence was close to that of the soil solution and was independent of soil texture.