The objective of this work was to evaluate the relations between soil water content and the soil bulk dielectric constant, and to study different waveguides of a TRASE soil water content analyzer that operates according to TDR principles. Non-destructive and destructive samples of two sites of different texture of a Dystrophic Yellow Latossol were collected and packed into 10 L containers, resulting in four replications for each texture and structure. Three different waveguides were built with rods of 0.15 m length, one with a capacitor at the beginning of the waveguide, one without a capacitor, with rods 0.009 m apart, and another without a capacitor, with rods 0.022 m apart. These waveguides, together with buriable standard ones supplied by tne manufactures with 0.20 m rods 0.022 m apart, were inserted in each sample. Soil water content was obtained by gravimetry and estimated by the TRASE analyzer, based on soil bulk dielectric constants using all waveguides during the soil drying process with water contents changing from 0.35 m³ m-3 to 0.10 m³ m-3. Three mathematical models were fitted to soil water content and bulk dielectric constant data. An exponential model was the most suitable in estimating soil water content as a function of bulk dielectric constant for the standard waveguide. All evaluated waveguides were feasible for use as long as they are previously calibrated.
calibration; waveguide; soil water content; time-domain-reflectometry
