Ziziphus lotus L. (Lam.) and Z. mauritiana Lam., as a widespread species in Tunisia, are well known for their medicinal and food uses. The aim of the present study was to screen the content of total polyphenols, flavonoids, and condensed tannins together with the radical scavenging capacity and the antimicrobial activity of leaves, fruits and seeds extracts of Z. lotus and Z. mauritiana from different localities. Results showed that leaves extracts presented the highest phenolic compounds content for both species. Furthermore, LC-ESI-MS analysis allowed the identification of 28 bioactive compounds regardless of species and organs, with the predominance of quinic acid and rutin. Leaves extract of Z. mauritiana possessed the highest total antioxidant capacity. The antimicrobial tests showed that leaves extracts of Z. mauritiana and Z. lotus from Oued Esseder exhibited the highest activity against four bacterial strains (Staphylococcus aureus, Listeria monocytogenes, Salmonella typhimurium and Escherichia coli). The main results showed that the studied species of Ziziphus genus are an excellent source of natural bioactive molecules that could be an interesting material for industrial and food purposes.

A method of determination of irrigation depth using a numerical model of crop response to irrigation and weather forecast was presented. To optimize each irrigation depth, a concept of virtual income, which is proportional to an increment in transpiration amount during an irrigation interval, is introduced. A numerical model that simulates water, solute, and heat transport and crop response is used in a numerical experiment. Results indicated that the optimized irrigation depth can be smaller than the value which attains maximum yield.

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Field studies were conducted on a sandy soil during autumn of 2010 and 2011 in an arid region of Tunisia to investigate the effects of nitrogen and irrigation regimes with saline water on yield and water productivity (WP) of potato (Solanum tuberosum L. cv. Spunta) and soil salinity. For the two years, irrigation treatments consisted in water replacements of cumulated crop evapotranspiration (ETc) at levels of 100% (I100, full irrigation), 60% (I60) and 30% (I30), when the readily available water in I100 treatment was depleted, while the nitrogen treatments (N) were 0, 100, 200, and 300 kg/ha (No, N100, N200, and N300). Results showed that soil salinity values remained lower than those of electrical conductivity of irrigation water (ECiw) and were the lowest under treatment I100 and the highest with I30 treatment. Relatively low ECe values were also observed under I60 treatment. The highest potato yields for the two years were obtained with I100 treatment. Compared to I100, significant reductions in potato yields were observed under I60 and I30 deficit irrigation treatments resulting from a reduction in tubers number/m² and tuber weight. The water productivity (WP) was found to significantly vary among treatments, where the highest and the lowest values were observed for I30 and I100 treatments, respectively. Potato yield and WP increased with an increase in nitrogen rates. The rate of 300 kg N/ha was seen to give good yield and higher WP of potato under full (I100) and deficit (I60) irrigation treatments. However, application of N adversely affected potato yield and WP, when N level applied above 200 kg N/ha at I30. The WP was improved by N supply, but its effect decreased as the irrigation level increased. The IWP at I100, which produced the highest potato yield, was 8.5 and 9.9 kg/m 3 with N300 but this increased to 11.9 and 15.6 kg/m 3 at I30 with N200, in 2010 and 2011, respectively. These re-* Corresponding author.F. El Mokh et al. 502sults suggested that potato in arid region could be cultivated with acceptable yields while saving irrigation water and reducing nitrogen supply but it was essential to exploit the interaction effect between these two parameters to maximize resource use efficiency.

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 EC i of 3.6 dS/m. Irrigation treatments consisted in water replacements of accumulated ET c 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 EC e 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.