Numerical Analysis of Soil Water Dynamics Under Subsurface Ring-Shaped Emitter Irrigation Using Hydrus.

A low-cost subsurface irrigation system is able to generate benefits for small-scale farmers who have scarce water resources. The subsurface ring-shaped emitter made from a rubber hose has been developed and introduced in Indonesia. It is one of the low-cost irrigation technologies based on indigenous materials and skills. After a rubber hose is bent into a ring shape with a diameter of about 20 cm, five 5-mm holes are drilled at even intervals. The entire ring-shaped hose is then covered with a permeable textile so that water can infiltrate uniformly around the emitter in all directions into soil. The water application rate is controlled by a water tank connected to the emitter. Because the ring-shaped hose is fully covered with the textile, it is not easy to detect if there is any malfunction and to repair it. To promote the subsurface ring-shaped emitter, it is important to make it easier to maintain. Because the number of experiments that can be carried out is limited, it is important that the performance of the ring-shaped emitter can be evaluated using numerical simulations. The main objectives of this study are therefore twofold. First, the performance of the current ring-shaped emitter was evaluated numerically with HYDRUS. Second, to propose a better design of the ring-shaped emitter, the effects of modified hole-configuration with different cover textiles was assessed numerically with HYDRUS. The first objective was achieved by comparing experimental results with numerical simulations. The results showed that the wetted regions around the emitter were well simulated regardless of the soil type and the applied water head. HYDRUS simulations in a full three-dimensional domain showed that, depending upon the soil type, the original ring-shaped emitter may wet the soil too much and the number of holes can be reduced significantly.