Yield Response of Drip-Irrigated Onion under Full and Deficit Irrigation with Saline Water in Arid Regions of Tunisia

A two-year study was conducted in arid region of Tunisia to evaluate the effects of deficit irrigation regimes with saline water on soil salinity, yield, and water use efficiency of onion grown in a commercial farm on a sandy soil and drip-irrigated with water having an EC𝑖 of 3.6 dS/m. Irrigation treatments consisted in water replacements of accumulated ET𝑐 at levels of 100% (SWB-100, full irrigation), 80% (DI-80), 60% (DI-60), when the readily available water in the control treatment (SWB-100) is depleted, deficit irrigation during ripening stage (SWB100-MDI60) and farmer method corresponding to irrigation practices implemented by the local farmers. Results on onion production and soil salinization are globally coherent between the two-year experiments and show significant difference between irrigation regimes. Higher soil salinity was maintained in the root zone with DI-60 and farmer treatments than full irrigation (SWB-100). SWB100-MDI60 and DI-80 treatments resulted also in low EC𝑒 values. No significant differences were observed in bulbs fresh and dry yields, bulbs number·ha−1 and weight from the comparison between full irrigation (SWB-100) and deficit treatments (DI-80, SWB100-MDI60). DI-60 irrigation treatment caused significant reductions in the four parameters considered in comparison with SWB-100. The farmer method caused significant reductions in yield components and resulted in increase of water usage 45 and 33% in 2008 and 2009, respectively. Water use efficiency was found to vary significantly among treatments, where the highest and the lowest values were observed for DI-60 and farmer treatments, respectively. The full irrigation (SWB-100) and deficit irrigation (DI-80 and SWB100-MDI60) strategies were found to be a useful practice for scheduling onion irrigation with saline water under the arid Mediterranean conditions of southern Tunisia.