Are soils like sponges?

The purpose of this paper is to explore the validity of the old analogy tha t "soil is like a sponge." Laboratory experiments were conducted to measure two hydrologic properties of porous media: drainage under gravity, and wat er potential curves. A tipping bucket rain gage connected to a data logger was used to measure the rate at which water drained under the force of grav ity from a trough filled with four saturated porous media - cellulose spong es, topsoil, peat, and a medium sand. Pressure plate techniques were used t o determine water potential curves for soil materials and sponges, in terms of relative cumulative discharge from the trough, sponges were intermediat e between peat and topsoil. Because of their tremendous water-holding capac ity, sponges discharged more than 2.5 times as much water as did peat. The water potential curve for sponges was fairly flat, like that of topsoil, bu t the high water content across all pressures (0.30-15.0 bars) indicated so me similarity to peat. The results of these experiments suggest that the ge neral patterns of water retention and release in soil materials and sponges are similar and vary only in degree.