Performance of Pitcher Irrigation Systems.

Pitcher irrigation is an ancient and efficient irrigation system used in many arid and semi-arid regions. Small pitchers are often used since they are less expensive than large ones.  However, questions exist about whether the patterns and extent of soil wetting obtained with small pitchers are comparable to those achieved with larger pitchers.  This work addresses these questions through a combination of experimental and simulation studies involving three pitcher sizes, identified here as size large (20 liters), medium (15 liters), and small (11 liters). Saturated hydraulic conductivities of the pitcher materials were measured using a constant head method; the measured values ranged from 0.07 cm d^-1 for the large pitcher to 0.14 cm d^-1 for the smaller sizes. To determine the zone of wetting, the pitchers were buried down to their necks in a sandy loam soil and filled with water. Water content distributions were determined after 1 and 10 days at locations 20, 40, and 60 cm away from the pitcher center at soil depths of 0 20, 40 and 60 cm.  Moisture distributions predicted with the HYDRUS-2D simulation model were found to be in close agreement with the experimental results, showing RMSE values between 0.004 and 0.023. The close agreement suggests that HYDRUS-2D is a suitable tool for investigating and designing pitcher irrigation systems. Experimental and numerical results showed that a small pitcher half the size of a larger one, but with double the hydraulic conductivity, will produce approximately the same wetting front as the larger pitcher. Simulations for the large pitcher further showed, as expected, more horizontal spreading of water in a fine-textured soil as compared to a coarse-textured soil.