The objective of this study was to determine the unsaturated hydraulic conductivity, using a neutron probe, of a clay sandy Oxisol. The study was carried out in the city of Piracicaba, State of São Paulo, Brazil (22º42' 43.3'' S, 47º 37' 10.4'' W, 546 m). The dimensions of the experimental plot were 45 m x 15 m, in which 40 aluminum tubes were installed in order to access a neutron probe to measure the soil water content at the depths of 0.2, 0.4, 0.6, 0.8 and 1.0 m and, then, calculate the soil water storage of the 0 - 1.0 m soil layer. The distribution of these tubes was made in grids of four columns by ten rows, in spacing of 5 x 5 m. The K( θ) ) functions were determined in the 40 points from regression analyses of θ as function lnt and h z as a function of lnt, being K the hydraulic conductivity, θ the volumetric soil water content, h z the soil water storage in the 0 -Z m layer, and t the soil water redistribution time. The neutron probe proved to be an efficient equipment in determining soil water contents, in the instantaneous profile method for determination of the K( θ) function in homogeneous soil.
hydraulic conductivity; instantaneous profile; soil water dynamics
