A Functional Model for Upward Flow From a Water Table and Its Redistribution.

The supply of water for plant use from poorly drained or artificially drained soils where a water table is present can be significant.  The saturated part of the profile below and near the water table also restricts downward root movement during vegetative growth of annual plants. Most widely used crop simulation models do not include plant water supply from a water table in soil water balance calculations.  We developed a functional routine for simulating upward flow (U) from a watertable using an empirical approach suggested by W. S. Meyer as reported in Ayars et al (2006).  After calculations of the daily water uptake by roots and upward movement by soil evaporation, U is added to the unsaturated soil layers above the watertable.  Starting at the lowest layer above the watertable, each layer receives a fraction of U such that the water content is equal to the water content of the soil matric potential calculated from the distance above the water table.  This procedure is done until a layer is reached where the supply of U is exhausted.  The characteristic curve for each layer is calculated using an empirical soil characteristic curve with emphasis on matrix potentials between saturation and DUL.