CRITICAL ANALYSIS OF THE FIELD DETERMINATION OF SOIL HYDRAULIC CONDUCTIVITY FUNCTIONS USING THE FLUX-GRADIENT APPROACH

The determination and the use of soil hydraulic conductivity functions obtained from internal drainage experiments, performed in field soil profiles, using the Darcy-Buckingham flux gradient approach are discus sed. Details of the calculation procedures indicate the sensitivity of the methodologies used, and of the most commonly adopted model for K( theta) relations: K(theta)=K-0.exp[-gamma.(theta(0)-theta)]. It is sho wn that the unit total water potential gradient cannot prevail in the whole soil profile during internal drainage after infiltration and tha t, as a consequence of this assumption, several methods of hydraulic c onductivity determination yield K(theta) relations which are depth dep endent, even for homogeneous soils. The difficulties of using K(theta) relations in modeling soil water dynamics due to their very strong ex ponential behaviour are also discussed. (C) 1998 Elsevier Science B.V. All rights reserved.