Relative water uptake rate as a criterion for trickle irrigation system design: III. Subsurface trickle irrigation.

摘要

The objective of this study was to apply a coupled source-sink modeling approach to subsurface trickle irrigation design, to determine the maximum possible relative water uptake rate and to evaluate its dependence on soil type, emitter depths, atmospheric evaporative demand, and rooting zone size. The early stage of plant growth (sink-above-source scenario) was modeled by placing a point sink of unknown strength between the soil surface (evaporating or nonevaporating) and a subsurface point source of given strength; for the subsequent stage of plant growth, i.e., most of the irrigation season, a point sink was located below the subsurface source. The principal approach involved determination of the relative water uptake by applying the maximum suction pressure (zero matric flux potential) at an isobar that bounds a conceived rooting zone domain. A major motivation for using subsurface drip irrigation is to reduce evaporation. This study shows that evaporation affects mainly the ratio of water loss by deep percolation to water loss by evaporation and that it has negligible influence on the water uptake rate. In the early-stage scenario, water uptake competes with gravitational forces. Therefore water uptake is generally small and decreases significantly with increasing root-system radius. In the late-stage scenario, the relative water uptake rate still decreases as the root system radius increases, but it remains larger than in the early-stage scenario. Some features of the flow field, with and without evaporation, are illustrated by plotting streamlines and contours of constant water saturation degree for these two scenarios.Digital Object Identifier http://dx.doi.org/10.2136/sssaj2009.0340