Among physical soil properties, hydraulic conductivity is one of the most important for studies which involve soil water movement. Establishing a relation between hydraulic conductivity and soil water content (K(θ) function) is essential for such studies. The method to determine the K(θ) function in a soil, called "instantaneous profile method", has one main advantage: it is based on direct field measurements with no need of awaiting the establishment of steady-state conditions. For this kind of experiment, no studies could be found about sensitivity to errors in experimental data or what influence one experimental observation more or less would have on the parameterization of the K(θ) function. Based on two instantaneous profile experiments (carried out on the 'Luiz de Queiroz' campus of the Universidade de São Paulo in Piracicaba, State of São Paulo, Brazil), this study tried to analyze the sensitivity of the instantaneous profile method to variations in field observations, using a computer algorithm for the analysis of the experimental data. The effect of the following modifications in the original data set were checked: removal of one observation; removal of final observations; error in the in the angular coefficient of the TDR calibration; error in the intercept of the TDR calibration; error in one of the TDR readings. Results show that the instantaneous profile method, together with the applied computer algorithm, has a high sensitivity to small uncertainties in the fitting of functions to soil moisture versus time. As it is also very sensitive to the zero time reading, which, therefore, should best not be considered. Errors or uncertainties in fitting soil water potential to depth proved to have a smaller influence on the final result. A not strictly exponential behavior between hydraulic conductivity and soil moisture increases the method's sensitivity to small errors. Errors in the angular coefficient or intercept of a TDR with linear calibration equation only affect the angular coefficient (γ) or intercept (ln(K*)) of the K(θ) function, respectively, when the matrix potential is determined by tensiometry.
hydraulic conductivity; field method