CALIBRAÇÃO DE SONDAS DE CAPACITÂNCIA PARA DETERMINAÇÃO DE UMIDADE EM LATOSSOLO VERMELHO DISTROFÉRRICO1

Abstract

Two capacitance probes (PR2/6, Delta-T Devices) were calibrated to a Dystroferric Red Latosol (Oxisol) in the Campus of Federal University of Lavras, MG. Access tubes were installed to monitor water content, so that a trench was opened up near the tube to collect soil samples. Equipment readings were performed for depth intervals of 10, 20, 30, 40, 60 and 100 cm, together with soil sample collection in order to determine volumetric water content (v). For each depth sample, a calibration equation was established. The highest adjustments of R2 were 0.877 and 0.793 in the 10 cm sensor, while the lowest adjustments of R2 were 0.312 and 0.415 in the 100 cm sensor. Depth sensors of 20, 30 and 40 cm in the 2 probes had similar R2 values. Values of the parameters (a1 and a0) of the calibration equation ranged from 4.475 to 10 for a1 and -0.017 to 0.789 for a0; 3.818 to 9.160 for a1 and -2.849 to 1.148 for a0 in the probes 1 and 2, respectively. The equation proposed by the manufacturer cannot be applied to all soils, therefore specific calibration is required for each soil.