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 discussed. Details of the calculation procedures indicate the sensitivity of the methodologies used, and of the most commonly adopted model for K(θ) relations: K(θ)=K0.exp[−γ.(θ0−θ)]. It is shown that the unit total water potential gradient cannot prevail in the whole soil profile during internal drainage after infiltration and that, as a consequence of this assumption, several methods of hydraulic conductivity determination yield K(θ) relations which are depth dependent, even for homogeneous soils. The difficulties of using K(θ) relations in modeling soil water dynamics due to their very strong exponential behaviour are also discussed.