Wetting Patterns and Relative Water-Uptake Rates from a Ring-Shaped Water Source.

A solution of the quasi-linear flow equation for steady and unsteady infiltration from a horizontal ring-shaped source with evaporation at the surface of a vertically heterogeneous soil is derived. A coupled source-sink approach enables analyzing the effects of geometrical source and sink attributes, potential evaporation rate and soil heterogeneity on wetting patterns and water-uptake rates. Ring emitters significantly smaller than the soil's capillary length behave like a point source and substantially larger rings behave like a line source. For ring source radii comparable to the soil's capillary length, water uptake depends on the ring radius and on the size of the root zone in a complex manner. At the stage of root development toward a ring emitter, water uptake is low, and it increases as the radius of the ring (torus)-shaped root system increases. Deepening a subsurface ring emitter decreases water uptake in the absence of evaporation from the soil surface and increases ater uptake in the presence of evaporation. It is suggested that the evaluated relative water-uptake rate be used as a design criterion for determining the desired radius and depth of the ring emitter with respect to root-zone geometry, soil properties and atmospheric evaporation demand. [ABSTRACT FROM AUTHOR]