Resumo

BRAVO-ESPINOSA, M.; SERRATO-BARAJAS, B.; FREGOSO-TIRADO, L.  e  MEDINA-OROZCO, L.. Empirical evaluation of the time domain reflectometry for water content measurement in two volcanic soils. Terra Latinoam [online]. 2009, vol.27, n.3, pp.171-176. ISSN 2395-8030.

Time domain reflectometry (TDR) is an indirect electromagnetic technique for measuring soil water content; it is fast, nondestructive, and accurate. However, the applicability of this technique particularly in volcanic and clayey soils was reported to be imprecise. The objective of this study was to evaluate the TDR manufacturer's calibration function, defined by the universal equation, in two different soils (Andisol and Acrisol), and furthermore, to estimate an empirical calibration function that is more accurate than the universal equation. A Trase System TDR model 6050X1 was used to estimate volumetric water content in two types of soils. Soil samples for gravimetric water content were collected with a screw auger, and soil bulk density was estimated by the excavation method. Weekly, measurements were made of water content by the TDR and gravimetric sampling simultaneously. The inequality coefficient was used to assess the deviation between the trend of predicted values (θ_Pred) by the universal equation and the trend of measured values (θ_Obs), whereas the discrepancy ratio was used to evaluate the universal equations ability to reproduce individual measured data. In both soils the relation K_a against θ_Obs deviated from the universal function defined by the relation K_a against θ_Pred; this deviation was greater in the Andisol than in the Acrisol; the universal equation underestimated the trend of measured values. Two calibration functions for the conditions of the two soils under study were obtained.

Palavras-chave : universal equation; Andisols; Acrisols; short-fallow system.

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