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.

An experiment on deficit irrigation of orange trees (Citrus sinensis, L. Osbeck, cv. Meski Maltaise) with saline water (1.5 g l‐1) was conducted in the arid region of Medenine, Tunisia. Four irrigation treatments were applied: full irrigation (FI), irrigated at 100% of the crop evapotranspiration; deficit irrigation (DI75) and (DI50), which received respectively 25 and 50% less water than FI; and the farmer's method (FM). Soil water content and salinity were monitored during the orange active period. Yield and fruit quality were measured at harvest and used to analyse water productivity (WP) and net income. Results show a decrease in soil salinity between the spring and winter seasons with maximum values observed for the DI50 treatment. Maximum yield levels were obtained under the FI treatment (26.6 t ha−1). Applying continuous deficit irrigation resulted in 24 and 45% yield reduction respectively for DI75 and DI50, compared to FI. Fruit‐quality parameters showed significant differences, with higher levels of total soluble solids for DI50 and better fruit weight for FI and FM. For total water supplies between 415 and 786 mm, WP was in the range 2.9–3.6 kg m‐3, with the highest values observed for the DI50 treatment and the lowest for FM. The soil water balance‐based irrigation method (FI) generated the greatest net income and the lowest soil salinization. Reduction in water supply produced an equivalent reduction in yield but a much stronger decrease in the economic return: using the DI75 strategy resulted in 25% water saving, 24% reduction in yield and 40% reduction in net income. Copyright © 2020 John Wiley & Sons, Ltd.

Field experiments were performed to study potato response to irrigation regimes using saline water on a sandy soil in southern Tunisia during the years 2011–2014. Irrigation regimes consisted in the replenishment of cumulated ETc when 35% of the root zone holding capacity is depleted at levels of 100% (I100), 70% (I70) and 40% (I40). The farmer used a fixed irrigation dose and interval, applying 16 mm every 4 days from planting till harvest. Higher soil salinity is observed at harvest under I40 and farmer treatments compared to I100. Highest potato yield was obtained with I100 treatment (24.4–27.5 t ha‐1) across 3 years. Significant reductions in yields were observed under I70 and I40 as compared to I100. The farmer's method also caused significant reductions in yield and resulted in using 15–22% more irrigation water than I100. Water productivity (WP) values varied between 4.3 kg m−3 (farmer) and 18.5 kg m−3 (I40) across different years and treatments. The scheduling technique using the soil water balance (SWB) with variable amounts is more efficient than the farmer's method. Full and deficit treatments (I100 and I70) generated the highest net income. I100 appears to be a promising irrigation strategy for the potato crop in the arid climate of Tunisia. Nonetheless, under water scarcity, irrigation of potato could be scheduled using I70 deficit strategy, with some yield reductions (12.5–23.0%). Copyright © 2016 John Wiley & Sons, Ltd.

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