The tensiometer is the most used instrument in the field to determine the soil water matric potential, so that the evaluation of its reading systems is very important. The purpose of this study was to evaluate different reading systems for the traditional field tensiometer traditional field tensiometer and it is justified because it will indicate the situation in which each system should be used. The experiment was carried out in a completely randomized factorial design (3 x 2 x 2 x 11), using three tensiometer reading systems (mercury manometer, Bourdon gauge and digital tensimeter with pressure transducer), two installation depths of the porous cup (0.2 and 1.0 m), two readings per day (morning and afternoon) during 11 days of readings, with four replications. The data were submitted to the F test (variance analysis) and the means compared by the Tukey test at 5 %. Besides, the systems were also evaluated using the statistical indicators Willmott concordance index, maximum error, mean absolute error, normalized root mean-square error, determination coefficient, coefficient of residual mass and efficiency, based on the mercury manometer as reference. It was concluded that (a) whenever the Bourdon vacuometer is installed at a particular hydraulic load in the tensiometer length, this should be considered in the matric potential calculation, (b) the Bourdon's vacuometer was more precise and efficient than the digital tensiometer and (c) the digital tensiometer overestimated the soil water matric potential in comparison to the mercury manometer and Bourdon's vacuometer.
mercury manometer; vacuum gage; pressure transducer