Generallized Coupiled Source-Sink Model for Evailuating Transient Water Uptake in Trickle Irrigation: II. Irrigation Scheduling Scenarios

The previously derived coupled source sink modeling approach for vertically heterogeneous cylindrical domains was extended to conditions prevailing when water uptake is controlled by diurnally time-varying, transpiration-driven plant resistance and by cyclic water applications, both leading to unsteady flow regimes in the rooting zone. Examples include simulations of diurnal variations in water uptake rates by plant roots (sinks) in homogeneous and vertically heterogeneous soils of various texture, under conditions of steady, continuous and unsteady water application, representative of various irrigation scheduling practices: pulsed, daily, and every few days. In coarse-textured, fast-responding soil, it is possible to meet the diurnal transpiration demand, but water losses through deep percolation are high. In soils of finer texture, daily short applications in the morning result in uptake patterns skewed toward morning, whereas all-day-long irrigation pushes the temporal uptake pattern toward the afternoon. In fine-textured soils irrigated every few days, similar water uptake volumes result from either prolonged, all-day, or short, morning applications, but the through-cycle uptake rates are more even with all-day applications.