Abstract

Unsaturated hydraulic conductivity (K) can be expressed as a function of soil water content (θ) or pressure head (h). Methods to determine K often give highly variable results, thus making it difficult to report values for K in a reliable manner. Due to the sensitivity of pore conductivity to pore radius, it can be expected that K expressed as a function of h shows less variability than expressed as a function of θ. To test this hypothesis, K was determined at several values of θ and h using the instantaneous profile method at 48 locations in the surface and a subsurface layer of a Typic Hapludox in Brazil. Results were analyzed considering the field values of K at the time of observation (Kt), at fixed values of θ (Kθ), and at fixed values of h (Kh). Results show that the coefficient of variation of Kθ is higher than that of Kh, especially in the surface layer, which suggests that, if one has the choice, it would be preferable to estimate soil water movement using measured h values, and using K(h), instead of measuring θ and using K(θ). We also show that the variability in Kt increases as the soil gets drier, while Kθ and Kh show more variability for wetter soil.

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