Hydraulic conductivity is one of the most important soil properties for studies dealing with infiltration, water movement within the soil profile and to plant roots and internal drainage. The availability of the function hydraulic conductivity x soil water content (K(θ)) is essential to these studies. However, little is known about the variability of the empirical parameters of this function. Aiming to contribute with information on the variability of these parameters, a study is described in which observations of hydraulic conductivity as a function of soil water content by the instantaneous profile method were made in twelve locations within an area of 1000 m². The equation used for K(θ) was K = K0.exp[γ(θ-θ0)], in which K0 and θ0 are K and θ values, respectively, for zero time of water redistribution. The measurements of soil water content and matric potential were performed for about 50 days in nine depths between 0.2 and 1.0 m. Results show coefficients of variation of about two to three for the majority of depths for the K0 values, while values for γ showed lower variation coefficients, between 0.2 and 0.5, the higher occurring close to the surface and the lower ones at greater depths. It is concluded that soil water content data fit very well to time by a potential equation, while total water potential fits very well to depth by a second order polynomial equation. Results suggest that a relationship between K and θ, determined by the instantaneous profile method in an area of a few square meters, is not representantive for a much larger area than that where it was determined.
Richards' equation; tensiometers; neutron probe