Development of Empirical Equations for Predicting the Dimensions of the Wetted Bulb Formed in Drip Irrigation of a Loamy Sand Soil (Case Study: The Qaem Abad Plain, Kerman)

As water is the most precious commodity in drylands, economizing its use is a matter of the utmost importance. Furthermore, drip irrigation has been proven to be a very efficient method of watering agricultural crops. Therefore, determination of the proper spacing of emitters with certain discharge capacity at specified pressure operated for a limited duration is a water saving strategy. To formulize the dimensions of the wetted bulb formed under each emitter, we studied the emitter discharge and duration of irrigation for a given volume water application. This experiment was carried out on a sandy loam soil at the Ghaeem-Abad Plain, in the Province of Kerman. The treatments were 3 discharge rates: 4, 8, and 24 liters per second per ha, and the different irrigation times (6 times related to emitter discharge). Twenty four hours after irrigation termination, when a relative steady state had been reached in the soil, we removed the laterals and emitters, dug trenches parallel to the laterals, and measured the dimensions of the wetted bulbs for different application rates and durations. We observed that for a given volume of water, the wetted radius on the soil surface was directly related to the rate of emitter discharge, while the depth to the wetting front was indirectly related to it. Prolongation of application for different emitter discharge rates increased both the radius and the depth to the wetting front. The wetting patterns were almost identical for the three discharge rates. The dimensions of the wetted bulb under emitters were directly related to the discharge rate. We have developed empirical equations, which predict the emitter spacing, the wetted radius on the soil surface, and application duration to supply the required water to a specified rooting zone.