Evaluation of an equipment of time domain reflectometry (TDR) for moisture registration in a loam soil

The technique of time domain reflectometry (TDR) is being used to monitor soil water content, but manufacturer's calibration does not necessarily agree with each specific soil condition. Therefore, it is important to assess the probe in each soil where its use be planned. In this study, an evaluation was carried out for a wide range of moisture content, in a fertirrigated loam soil located at the experimental field at the School of Agronomy in Maracay, Venezuela, comparing the volumetric water content (VWC) obtained by TDR with the VWC determined in soil samples taken depth 10 cm and 20 cm below the soil surface. It was found a strong lineal correlation between VWC measured in samples and VWC obtained by TDR probe (r = 0.88 for depth 10 cm and 0.95 for depth 20 cm; respectively). Otherwise, regression equations (R-2 adjusted = 77.6% for depth 10 cm and 90.5% for depth 20 cm) showed that TDR must overestimate soil water content; its lectures were higher (140-1.48% in top 10 cm and 164-170% in top 20 cm) than those were measured in soil samples, making it clear calibration is necessary.