Coupled Source-Sink Model for Evaluating Temporal Water Uptake Patterns in Trickle Irrigation.

A recently proposed approach for the design of the geometry of trickle irrigation systems (Communar and Friedman, 2009), based on modeling steady water flow and uptake, provides the maximum possible root water uptake for given source-sink geometries and soil types. In this lecture, the coupled source-sink modeling approach is extended to conditions of transient irrigation. Two types of transient processes are considered: one due to cyclic water application from surface sources and another one due to diurnal variations in water uptake rate by the plant roots. Daily water applications are simulated using a time-dependent solution for cyclic surface point sources and the time-dependent water uptake process is simulated using a steady state solution for a sub-surface point sink of a local, plant resistance that varies in a daily cosine mode. The time-dependent water uptake rate and the overall water uptake during transpiration time are both analyzed with the model. The results indicate that in fine-textured soils the time-dependent water uptake rate does not practically dependent on the duration (and source strength) of the water application. However, for sandy soils the shorter the water application, the lower the predicted water uptake rate. Thus, an important factor determining the relative water uptake in sandy soils is the starting time of the water application. Optimal conditions for water uptake in such coarse-textured soils are reached when the pick of the wave of the soil water content created by the source passes through the rooting zone at a time which coincides with the minimal plant resistance.