Soil water retention and characteristic curve

The relations between the amount of water retained in unsaturated soils and the retaining capillary and adsorptive forces are described by the soil water characteristic (SWC) curve. This function is soil specific and plays an important role in many agricultural, environmental, and engineering applications. A soil specific SWC is used for crop water management and determining plant available soil water, for representing water flow and contaminant transport, and for assessing natural disasters such as flooding or landslides. This chapter presents fundamental and novel concepts and techniques for representation and quantification of the SWC curve and estimation of its parameters at local and global scales. Standard measurement methods such as the Richards pressure plate apparatus and Tempe cells are presented along with contemporary techniques based on chilled-mirror dewpoint psychrometry, dielectric measurements and dynamic evaporation. We review different pore space representation models, the concept of hysteresis, and discuss adsorptive forces that dominate the dry end of SWC.