Use of TDR probes to estimate soil moisture and electric conductivity [Sondas de TDR para a estimativa da umidade e da condutividade elétrica do solo]

Abstract

In Brazil, TDR use is relatively recent and several studies have been done to adequate this technique to different soil types. TDR use implies in a high financial cost for the Brazilian agriculture, mainly the purchase of equipment and probes. Because of that, this study aimed to present the building of three different kinds of TDR probes that may substitute the ones available in the market. The performance for each probe was evaluated considering soil moisture estimate and electric conductivity. The three proposed probes are the following ones: continuous probe with three posts, segmented probe with multiple posts and the one with coaxial cable and variable volume. The following parameters were considered in this evaluation: reflection coefficient, characteristic impedance and spatial sensitivity. The results showed that these proposed TDR probes may be used for soil moisture and electric conductivity estimates. Their use is an alternate method to the commercial ones, and it allows TDR use in different conditions, mainly when a larger number of TDR probes are necessary.