Water Retention: Laboratory Methods

The water content, solution phase content, or wetness of the soil may be expressed on a weight, volume, or degree of saturation basis. For analysis of water flow in soil profiles, the volume basis is most useful. The water retention function is primarily dependent upon the texture or particle-size distribution of the soil, and the structure or arrangement of the particles. The soil-water system is in hydraulic contact with the body of water via a water-wetted porous plate or membrane. Water retention measurements on subsoils, especially those in which there is a significant degree of structural development, should be made on "undisturbed" core samples. The chemical composition of the wetting fluid can affect the water retention of the samples, particularly in fine-textured soils that contain significant amounts of swelling clays. The intensity of the forces retaining the water in the soil at a given matric pressure head is temperature-dependent.