CALIBRACIÓN DE LA SONDA TDR-300 PARA MEDICIONES DE HUMEDAD DEL SUELO EN SAN RAFAEL DE ONOTO, ESTADO PORTUGUESA* Probe calibration for TDR-300 for measurements moisture soil in San Rafael de Onoto, Portugesa State

The method for determining the water content in the soil through probes TDR (Time Domain Reflectometry) estimated the water content based on the Ka (dielectric constant) using a polynomial equation. However, calibrations should be conducted on site, leading to roles of individual calibration for each soil type. With the objective to calibrate the probe TDR-300 for use in monitoring the progressive moisture content of soil in the farm 2D-18 at San Rafael de Onoto municipality, Portuguesa State, 48 measurements were made of the Ka, using 7 cm rods and compared with gravimetric contrast, collected from soil samples in each of the measuring points for the superficial (E1), medium (E2) and deep (E3) layers at depths 0-20, 20-40 and 40-60 cm, respectively. It was determined the texture, bulk density, correlation coefficient and calibration curve for each stratum. The correlation coefficients was 0.72, 0.43 and 0.46, respectively. There was evidence of over and under estimation of gravimetric moisture in humidity levels below 14% and above 24% to E1 and E2, while at E3 there was not evidence of any adjustment. We conclude that the probe TDR-300 can be used in E1 and E2, with values of Ka between 2.500-3.700 y 2.700-4.000 uS/cm, respectively.