AN ANALYSIS OF SOIL HYDRAULIC CONDUCTIVITY DETERMINATION BY MEANS OF THE INSTANTANEOUS PROFILE METHOD

The soil hydraulic conductivity K is a property that expresses the ability of the soil in conducting water. It is important for soil management, crops yield and the preservation of soil and environment. The soil hydraulic conductivity can be determined by means of laboratory and field methods, the first better experimentally controlled and the second with less degree of soil disturbing. Among the field methods, the instantaneous profile one is the most used, both the original and the modified in which a relation between the soil water content theta and the soil water redistribution time t is obtained assuming soil water total potential gradient equal to one. In order to analyse in more detail the method, a study was carried out with the objective of verifying the possibility to obtain the relation of theta as a function of t without the assumption of the existence of total potential gradient equal to one. The study was developed with data of four soils and the validation of the proposed relation was made by comparing the K(theta) function obtained from it and the K(theta) function obtained in the traditional way. From the results, it could be conclude that the proposed relation between theta and t for the instantaneous method showed to be valid and that the total potential gradient may affect both gamma and K-0 parameters of the K = K(0)exp [gamma(theta - theta(0))] equation fitted to the experimental data. For the specific case of the soils evaluated in this work, the potential gradient had low influence on the gamma parameter as compared with its influence on the K-0 parameter, leading to the possibility of utilization of a mean potential gradient to obtain the K(theta) function. Besides, it was observed that the procedure to calculate the flux density from the curve of soil water storage as a function of redistribution time is much simpler than the original that has been used for this purpose in the instantaneous profile method.