ABSTRACT
In subsurface drip irrigation (SDI), water emits from the buried drippers into the soil and spreads out in the rhizosphere due to capillary and gravity forces [20, 25]. Thus, SDI system permits direct application of water to the wetted soil volume and maintaining dry the nonrooted topsoil. This pattern has advantages such as minimizing soil evaporation, deep percolation, weeds growth and thus affects evapoconcentration phenomenon. The SDI improves the water application uniformity, increases the laterals and emitters longevity, reduces the occurrence of soil-borne diseases, and infestation of weeds. Several field trials have revealed relevant profits due to adequate management of SDI for crop production. Nevertheless, the appropriate depth of buried laterals remains debatable [10, 14, 21, 28]. Comparing evaporation from surface and subsurface drip irrigation systems, Evett et al. [7] reported a saving of 51 mm and 81 mm irrigation depth with drip laterals buried at 15 cm and 30 cm, respectively. Neelam and Rajput [20] recorded maximum onion yield (25.7 t per ha) with drip laterals buried at 10 cm depth. They reported maximum drainage with drip laterals at 30 cm depth. Several investigators have analyzed the effects of soil properties on the discharge of SDI emitters and water distribution uniformity [1, 17, 23]. The analytical method by Sinobas et al. [25] predicted reasonably well the soil water suction and the pressure head distribution in the laterals and SDI units [26]. The water oozes out from the buried emitters due to inlet lateral pressure head and the soil water suction. Therefore, the emitter discharge is high at the beginning of irrigation due to dry root zone. Gradually, as the soil pore space in the vicinity of the dripper outlet is filled with water, a positive pressure head develops, which may cause a decrease in dripper discharge [24]. If the discharge is greater than the soil infiltration capacity, the resulting overpressure near the nozzle tends to reduce the flow rate [17, 30].
