TEXTURE AND ELECTRICAL-CONDUCTIVITY EFFECTS ON TEMPERATURE DEPENDENCYIN TIME-DOMAIN REFLECTOMETRY

If not accounted for, temperature effects on the water content and ele ctrical conductivity measured with time domain reflectometry (TDR) wil l introduce significant errors. In this study, an automated TDR system was used to quantify the temperature dependence of the apparent diele ctric constant and electrical conductivity in wet soils. Sandy, clayey , and organic soils were used to examine the effect of soil texture. T he temperature correction factor for water content measurements was pr edicted, by using different dielectric mixing models, to lie between - 0.00253 and -0.00419 theta degrees C-1, the negative value of the temp erature correction factor indicating a decrease in the water content m easurements 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 so ils, however, the temperature dependence was significantly lower, Larg e specific surface combined with high soil solution electrical conduct ivity resulted in a positive correction factor, i.e,, water content me asurements increased with increases in temperature, The temperature de pendence of the bulk electrical conductivity was investigated using di fferent soils and soil solutions. The temperature dependence was close to that of the soil solution and was independent of soil texture.