Modeling Water Distribution Pattern around Subsurface Drippers in a Sandy Soil and Estimation of Evaporation in such Systems

Water scarcity and the need to obtain the highest water use efficiency have encouraged installation of subsurface drip irrigation systems in the pistachio orchards in the hyper-arid southeastern I.R. Iran. As the economics dictate system design optimization, the water distribution pattern around drippers should be determined accurately. We used the highly regarded HYDRRUS-2D software, which simulates water, salt and heat transport under both saturated and under saturated conditions both during and after termination of irrigation, to estimate water distribution pattern around drippers installed at a depth of 30 cm in a sandy soil. Plastic mulching was also included in the treatments. The discharge rates were 2 and 4 liters per hour. The model satisfactorily simulated water redistribution in the soil profile 24 hours after irrigation termination (R2=0.92, RMSE=0.0192). Increasing the discharge to 6 liters per hour resulted in the reduction of the wetted bulb diameter. This will entail a reduction in the lateral spacing, thus an increase in the cost of the irrigation system. Covering the area above the drippers with plastic mulch reduced potential evaporative losses due to maintaining a higher relative humidity under the cover.