Subsurface drip irrigation (SDI) is one of the most promising irrigation systems. It is based on small and frequent water supplies. Because SDI emitters are buried, their discharges are dependent on the water status at the vicinity of the outlets. This paper was targeted to design the SDI laterals accounting for the soil water-retention characteristics and the roots water extraction. The proposed approach provides systematic triggering and cut-off of irrigation events based on fixed water suctions in the vadose zone. In doing so, the soil water content is maintained at an optimal threshold ascertaining the best plant growth. Knowing the soil water-retention curve, the appropriate water suction for the plant growth, and the emitter discharge-pressure head relationship, the developed method allows the computation of the required hydraulics of the lateral (e.g., inlet pressure head, inside diameter, etc.). The proposed approach is a helpful tool for best SDI systems design and appropriate water management. An illustrative example is presented for SDI laterals’ design on tomato crop. 1. Introduction In subsurface drip irrigation (SDI), water seeps from the buried emitters into the soil and spreads out in the vadose zone under the conjugate effect of capillary and gravity forces [1, 2]. Thus, SDI system allows the direct application of water to the rhizosphere maintaining dry the nonrooted topsoil. This pattern generates numerous advantages such as minimizing soil evaporation and then evapoconcentration phenomenon. The rationale is that SDI improves the water application uniformity, increases the laterals and emitters longevity, reduces the occurrence of soil-borne diseases, and allows the control of weeds infestation. Several field trials revealed relevant profits on managing SDI for crop production. Nevertheless, the appropriate depth of buried laterals remains debatable [3–6]. Comparing evaporation from surface and subsurface drip irrigation systems, Evett et al.  reported that 51？mm and 81？mm were saved with drip laterals buried at 15？cm and 30？cm, respectively. Neelam and Rajput  recorded maximum onion yield (25.7？t？ha？1) with drip laterals buried at 10？cm. According to these authors, the maximum drainage occurred when drip laterals are laid at 30？cm depth. On the other hand, numerous studies were devoted to the analysis of the effect of the soil properties on the SDI emitters discharge and water distribution uniformity [8–10]. The analytical approach proposed by Sinobas et al.  predicts reasonably well the soil water suction and the pressure
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