Surface irrigation performance of date palms under water scarcity in arid irrigated lands

In this paper, a study on the performance of surface irrigation of date palms in a Tunisian arid area (Douz oasis) is presented. The study is conducted in 16 plots with various sizes and soil textures over a 4-year period (2012–2015). In the first step, an assessment of total water requirements of the date palms is carried out. Then, the surface irrigation performance is analyzed using three indicators, i.e., the relative water supply (RWS) indicator, the uniformity index of water distribution (DU), and the water application efficiency (Ea). Finally, the irrigation management problems are identified. The results indicate that in the arid Tunisian Saharan oases, the soil texture, plot size, and farmers’ practices (especially irrigation duration) have significant effects on surface irrigation performance. The average annual net irrigation requirements of date palms are about 2400 mm. The RWS increases from 1.8 in the smaller plots (0.5 ha) to 3.6 in the largest plots (2.5 ha), implying that the increase in the plot size requires an excessive water supply. DU decreases from 80.7 in the 0.5 ha plots to 65.4 in the 2.5 ha plots; however, no significant difference in the Ea is observed. The results show that the soil texture has no influence on the RWS and DU, but the Ea is significantly higher in the loamy-sand soils (46.7%) compared to the sandy soils (36.3%). Overall, RWS indicator is higher than 1 (RWS = 2.6) implying excessive irrigation supply to the system. Although DU is relatively uniform (> 60%), Ea is relatively low (< 50%) indicating that the current irrigation management is inefficient. These findings have a paramount importance for improving irrigation water management in the Tunisian Saharan oases