APPLICATION OF THE TDR TECHNIQUE IN TROPICAL SOIL

One recent technology developed to estimate soil water content is the TDR principle (Time Domain Reflectometry), where the determination of the calibration curve for each soil type is recommended (volumetric water content (q) versus apparent dielectric constant (Ka)). The use of this principle in tropical soils can be a problem since the available equations in the literature seemingly do not consider the differences of the soil, mainly the presence of iron oxide. Silva (1998) concluded that it could affect the magnetic field created by electric pulse, and consequently affect the time of displacement of the emitted wave. The objective of this work was study the limitations to develop a calibration equation to Red Oxisol soil in tropical conditions. Two methodologies were used to determine the calibration equation: the first one, for laboratory conditions, described by Tommaselli (1997) used deformed soil samples, and the second one developed for field condition. The results were compared to the Topp Equation (Topp et al., 1980). The advantages and limitations of each procedure were analyzed and technical recommendations were defined. The results showed the field condition method presented the smallest deviations compared to the water content determined by the gravimetric method. The laboratory method and the Topp equations did not explain satisfactorily the results observed.

SOUZA, C. F.; MATSURA, E. E.; TESTEZLAF, R.   
UNICAMP/Feagri - Departamento de Įgua e Solo
Brazil