Calibration of FDR and TDR probes to estimate water content in two types of soil [Calibração de sondas FDR e TDR para a estimativa da umidade em dois tipos de solo]

Abstract

A tendency exists towards using indirect methods to estimate soil water content (soil moisture - θ) in the field, due to the easy of handling and agility for data acquisition. For soil moisture estimates, calibration curves are recommended for each type of soil. The objective of this study was to evaluate and calibrate FDR (Diviner2000) and TDR probes to measure moisture in two types of soil with different textures. Under laboratory conditions, variations in soil moisture determined by FDR, TDR and the standard (gravimetric) methods were compared. Values of soil moisture showed that readings using FDR method underestimated the values, and those using TDR method overestimated them when compared with those of the standard method. However, TDR values were lower to those of the standard method. Indirect methods proved to be acceptable for monitoring soil water, and the results showed that they can replace the standard method when accuracy is not essential.