In the Canary Islands the price fluctuation of groundwater (0.3 to 0.7 €/m3), which is a private resource, often limits the recovery of the agricultural investments. Availability of alternative resources (reclaimed water: RW, desalinized seawater: DW and desalinized reclaimed water: DRW) at a foreseeable price will allow people to design the optimal infrastructures adapted to their needs The pumping cost is included in the “public” water price of DW (0.6 €/m3), RW (0.2 €/m3) and DRW (0.42 €/m3), but only if it is under 300 m of altitude. As a subsurface irrigation system (SDI), uses the soil as a natural advanced (but not high cost) water treatment, the in situ reuse of RW produced by lower tech wastewater plants would provide a valuable resource for the small villages.
A successful study case is presented here. A 2-year SDI experiment was performed using RW, cultivating alfalfa (Medicago sativa) and Sudan grass hybrid (Sorghum bicolor ssp sudanense). Although a saline (EC: 2.24 dS/m) and sodic (SAR: 6.9) water was used, irrigation with SDI led to high forage yields (between 8.4 and 11.9 kg of fresh matter/m2 obtained by 8 harvests per year). However, sand filter and drip lines have to be cleaned weakly and every 6 months respectively. As a conclusion of this study, adequate plant germination and yields, and feasibility of SDI using a secondary effluent was demonstrated. Besides, water cost represents only 24 to 17 % from the gross income.