Deficit Irrigation Using Saline Water of Fruit Trees under Water Scarcity Conditions of Southern Tunisia

Both water scarcity and salinity are major obstacles for crop production in arid parts of Tunisia and require adoption of strategies aimed at improving water-use efficiency. Field experiments on deficit irrigation (DI) of table olive, orange trees, and grapevines with saline water (2 dS m  1) were conducted in the arid region of M denine, Tunisia. Three irrigation treatments were compared with the farmer’s method (FM) over two years (2013–2014): deficit irrigation (DI75) and (DI50), which received 75% and 50% less water than full irrigation (FI), respectively, and full compensation of the crop evapotranspiration (FI). Measurements included seasonal changes in soil water content, soil salinity, yield, fruit quality, and economic return. Results showed that in-season water limitations, roughly between 700–250 mm, caused significant reductions in yield and fruit weight, but improved the total soluble solids of fruits. Under FI, DI75, DI50, and FM, average yields were 26.6, 20.1, 14.7, and 21.2 t ha  1 for orange, 4.5, 4.0, 3.1, and 3.5 t ha  1 for table olive, and 3.8, 3.4, 3.1, and 3.5 t ha  1 for grapevine, respectively. Soil salinity build up increased linearly with decreasing irrigation water. Irrigation water productivity (IWP), although lowest for FM, was relatively high (3.30–4.30 kg m  3 for orange, 0.65–1.20 kg m  3 for table olive, and 0.74–1.30 kg m  3 for grapevine). Economic evaluation showed that the FI strategy generated the greatest net income (1800–6630 USD ha  1), followed by DI75 (1350–3940 USD ha  1), FM (844–4340 USD ha  1), and DI50 (600–2400 USD ha  1). The results show an important potential for reasonably sustaining farmer’s income under increased water scarcity.