SOIL SURVEY INTERPRETATIONS FROM WATER RETENTION DATA: I. DEVELOPMENT AND VALIDATION OF A WATER RETENTION MODEL.

The prediction of spatial and temporal variations in the soil water regime provides the basis for a proposed soil survey interpretive system. A water retention model estimates the boundary desorption curve from saturation to pF 4. 2 for mineral soils in situ using limited soil physical data (standard error of estimate less than 2. 2% g g** minus **1). The total porosity (structural parameter) and clay content (adsorptive parameter) define the position of the moisture characteristic in logarithmic coordinates and the silt content its configuration. Organic matter affects the structural parameter by reducing both the dry bulk and particle densities but only significantly influences the adsorptive parameter at organic matter contents of 5% or greater. Model validation shows that the state and quantity of water retained by field soils near equilibrium is dependent on the position of the phreatic surface.