SCIENCES of SOILS, Rel. 2, 1997 -

Replacing the field capacity concept by an internal drainage approach
A method for homogeneous soil profiles

Steffen Zacharias and Klaus Bohne

Institut für Bodenkunde, Universität Rostock, Justus-von-Liebig-Weg 6, 18051 Rostock, Germany


Key Words

field capacity, soil water storage, water retention, internal drainage, unsaturated water movement, parameter estimation


A physically based method to calculate the soil water storage for drained homogeneous profiles is presented in this paper. This method views soil water storage as a problem of internal drainage and considers the effects of ground-water depth and hydraulic conductivity on the amount of water stored.
Typical water retention curves for all of the (German) soil textural classes were used to determine VAN GENUCHTEN parameters. Volumetric soil water contents were estimated for every textural class after a drainage of 10 days time and for a suction head of 60 cm (common equivalent suction head for field capacity). The drainage of ground-water affected profiles was calculated using a special solution of RICHARDS-equation. A unit gradient method was used for soils with large ground-water depths. The results differ clearly from field capacity values in common soil science reference rules. The paper shows how non-steady-state behaviour of internal drainage affects soil surveys and assessment.