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Water scarcity is a limiting factor for agricultural development. Accordingly, the improvement of its efficiency is indispensable through the application of adequate irrigation strategies including deficit irrigation. In this context this work was undertaken. A field experiment have been carried out in Beni Khdache, south of Tunisia on grapevines to evaluate the agronomic responses, in terms of crop development, yield, yield quality and water productivity, under different water regimes. The first treatment (T100) consisted in delivering to the crop 100% of the ETc. The other two treatments (T75 and T50) consisted in delivering only 75 and 50% of the total real needs of the crop respectively. The fourth treatment (T0) was irrigated according to the farmer's recommendations. The results show a significant effect of the deficit irrigation on the vegetative growth of the grapevines in terms of berry weight. This difference had later a significant impact on the final yield. The highest yield (14t/ha) was found with full irrigation (T100). The farmer's method led to a significant drop in yield (40%) compared to the full irrigation treatment. Trees under water deficit (T75, T50) responded with an accumulation of sugars (17.3 °Brix and 16.8° Brix respectively) and a slight decrease in fruit acidity (3.9 and 3.8 respectively) compared to the T100 treatment (15°Brix,4) . The difference in irrigation water productivity of the grapevines obtained with the deficit irrigation treatments (T75, T50) is not significant compared to that of T100. The low water productivity was observed for the T0 and T75 treatments (1.9kg/m3 and 2.4 kg/ m3 respectively), while the highest values were obtained with the T50 and T100 treatments (2.8 kg/m3 and 2.6 kg/m3). These results indicate that full irrigation (T100) seems to be an adequate irrigation strategy for grapevine production under Tunisian arid conditions. Under water scarcity conditions, deficit irrigation with a 25% reduction in inputs (T75) is recommended for grapevine management. The T75 deficit irrigation treatment allows to save large amounts of irrigation water (25%) and to improve water productivity but accepting a certain yield drop.Keywords: Full irrigation, deficit irrigation, grapevine, yield, water productivity, arid environment, farmer's practices

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 Médenine, 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.

Irrigation management toimprove smallholder’s incomes for saline conditions Fathia El Mokh 1*, KamelNagaz 1, Mohamed Moncef Masmoudi2, Netij Ben Mechlia21Institut des Régions Arides, 4119 Médenine, Tunisia2INAT, 43 avenue Charles Nicolle, 2083 Tunis, Tunisia[*]ABSTRACT Abstract: In the Mediterranean arid regions, the water limitation is the constraint major for agriculture development. Under this condition, one of the most common water quality concerns for irrigated agriculture is saline. The use of this saline water is increasing with the increasing of water scarcity. Its use without integrate management (soil, crop and water) poses high risks of land degradation and crop productivity reduces. Therefore, this study was considered in southern Tunisia to investigate farmer irrigation practices over two years. The impact of irrigation strategies with saline water (6 dS/m) on yield, soil salinity, water productivity and farmer net return were evaluated. Five crops were considered: barley, carrot, fava bean, pepper and potato. The irrigation strategies based on soil water balance method (SWB) which are full irrigation strategy (FI: restore 100% of the crop evapotranspiration) and deficit treatment (DI70: 70% of the ETc covered) were compared to farmer practice (FM). For both seasons, FM strategy caused a significant increase in soil salinity that affects considerably the yield produced for most of the crops compared to the full and the deficit (30%) water supply strategies. The water restriction of 30% improves the total water productivity without affecting yield significantly especially for barley and faba bean where the yield reduction was ranging from 2.5 to 9.5%. Results showed that the practice of cash crops (potato, carrot and faba bean) which have a short cycle improves considerably the farmer incomes compared to the barley crop. The pepper provides also high economic return for farmer but it consumes more water and has a long growing cycle. Based on this analysis, the farmer income can be improve considerably with better irrigation and crop management. Key words: Water management, Salinity, Yield, Waterproductivity, Farmer return. [*] Corresponding author: elmokh.fa@gmail.com

The deficit irrigation (DI) as an on-farm water management strategy was tested for 3-years to determine the water requirements and productivity, soil salinity and yield for carrot irrigated with saline water (3.6 dS/m) under actual farming conditions in southern Tunisia. The irrigation regimes were full (I100) and deficit (I80 and I60) irrigated with levels of 100, 80 and 60% of ETc when the readily available water, 35% of total available water (TAW), in the I100 treatment was depleted, and traditional farmer practice (Farmer). Regulated DI regime where 40% reduction is applied only during ripening stage (I60-ripening) was also used . Higher soil salinity is observed at harvest under I60 and Farmer treatments compared to I100. Carrot yield was highest over 3 years for the I100 scheduling technique, (29.5, 28.7 and 26.8 t/ha) although no significant differences were observed with the I60-ripening strategy . However, the I80 and I60 treatments caused significant reductions in carrot yields through a reduction in roots number and weight in comparison with I100. The farmer’s method not only caused significant reductions in yield but also resulted in using 43 to 57 % more water and increased soil salinity. For all treatments, carrot yields were higher in first than the two following years. Water productivity (WP) values reflected this difference and varied between absolute extremes of 3.3 and 9.7 kg/m 3 . WP was the greatest in the I60 treatment and the least in the Farmer's strategy. I100 irrigation strategy provides significant advantage on yield and WP compared to farmer’s method in carrot production. Therefore, for water-saving purposes, the I100 irrigation scheduling is recommended to optimize the use of saline water in carrot production and to control soil salinity. Nonetheless, under water scarcity, irrigation of carrot could be scheduled using I60-ripening and I80 deficit strategies, with some yield reductions (4-15%).

The influence of deficit irrigation (DI) with saline water on soil salinity in a drip-irrigated potato and millet fields was investigated. We had compared proportional soil salinity developed under Full and DI under drip irrigation. For both experiments, the treatments were (1) Full, control treatment where rooting zone soil water content was increased to field capacity at each irrigation; (2) DI80; (3) DI60 and DI40; 20, 40 and 60% deficit irrigation compared to Full treatment were applied, respectively. Soil salinity was assessed using the isosalinity maps constructed with grid soil sampling of plant root zone at harvest. Results show that high spatial variability was observed in salinity along soil profiles when applying saline water with drip irrigation for potato. For the DI40 and DI60 treatments, high soil salinity was recorded in the upper soil layer close to the emitter. Increase of soil salinity within soil depths of 30 cm or below was also observed under DI60 and DI40 treatments. The lowest increase was noted under the full treatment. Surface soil salinity was somewhat higher under DI60 and DI40 compared with that of full and DI80 irrigation treatments. The distribution of salts around the dripper changes during the crop season according to applied irrigation treatments, with overall higher concentrations between the drippers and towards the margin of wetted band. Iso-salinity maps at harvest of potato showed that the surface layer of 30 cm depth had the lowest salinity which gradually increased at deeper zones irrespective of the treatment. Salt accumulation essentially occurred at wetting front between the drippers and the plant row. Although salt accumulation was relatively highest along the row under DI treatments, the area of accumulation was relatively shifted toward the center between the rows and the drip line. The results also show the importance of the potato cropping season to benefit from the leaching of soluble salts with the received rainfall. For millet experiments, salinity was lowest under emitters and highest midway to the margin of wetted bands and higher soil salinity was maintained in the root zone with deficit irrigation treatments than full irrigation. Millet and potato yields were highest under Full treatment. Yields decreased almost linearly when applied water was reduced. However, reduction in quality was significantly important for DI60 and DI40. The analysis outcome of the crops sensitivity to salt indicated respectively for autumn, winter and spring potato and millet crops that thresholds are close to the value calculated from published salt tolerance data (1.9, 1.55, 1.85 vs. 1.7 dS/m for potato and 3.46 vs. 3.65 dS/m for millet) but the slopes are considerably steeper (34, 54, 47 vs. 12%; 17 vs. 6.7%), apparently because of the combined effect of salinity and water stresses. The results provide information’s to farmers for formulating improved planning regarding irrigation management practices. The results support the practicality of using the full irrigation (100% of ETc) methodology to optimize irrigation with saline water for potato and millet production and to control soil salinity. Under situations of water shortage, the deficit irrigation strategy (DI80 and DI60) is recommended as a tool to schedule irrigation of potato and millet crops in arid regions of Tunisia.

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/m3 with N300 but this increased to 11.9 and 15.6 kg/m3 at I30 with N200, in 2010 and 2011, respectively. These results 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.

Field experiments were conducted on a sandy soil during spring of 2009 and autumn of 2010 in southern Tunisia for evaluating the effects of two drip irrigation methods and three irrigation regimes on soil moisture and salinity, yield and water use efficiency of potato (Solanum tuberosum L.). The surface drip (SDI) and subsurface drip (SSDI) irrigation methods were used. Irrigation regimes consisted in replacement of cumulated ETc when readily available water is depleted with levels of 100% (FI100), 60% (DI60) and 30% (DI30). FI100 was considered as full irrigation while DI60 and DI30 were considered as deficit irrigation regimes. Well water with an ECi of 7.0 dS/m was used for irrigation. Findings are globally consistent between the two experiments. Results show that soil moisture content and salinity were significantly affected by irrigation treatments and methods. Higher soil moisture content and lower soil salinity were maintained with SSDI than SDI for all irrigation treatments. For both irrigation methods, higher salinity and lower moisture content in the root zone are observed under DI60 and DI30 treatments compared to FI100. Potato yields were highest over two cropping periods for the SSDI method although no significant differences were observed with the SDI. Irrigation regimes resulted in significant difference in both irrigation methods on yield and its components. Yields were highest under FI100. Compared to FI100, considerable reductions in potato yields were observed under DI60 and DI30 deficit treatments resulting from a reduction in tubers number/m² and average tuber weight and size. Water use efficiency (WUE) was found to vary significantly among irrigation methods and treatments and varied between 5.9 and 20.5 kg/m3. WUE of SSDI method had generally higher values than SDI. The lowest WUE values were observed for the FI100 treatment, while the highest values were obtained under DI30 treatment for both methods. SSDI method provides significant advantage on yield and WUE and reduces the soil salinity compared to the SDI in potato production under experimental conditions. The SSDI and FI100 irrigation techniques seem to optimize the use of saline water in potato production and to control soil salinity. Under situations of water shortage, adopting deficit irrigation treatment (DI60) could be an alternative for irrigation scheduling of spring and autumn potato under the arid conditions of southern Tunisia.

Field studies were conducted for three years to determine the effects of irrigation regimes with saline water (3.6 dS/m) on soil salinity, yield and water productivity of carrot and millet under actual commercial-farming conditions in the arid region of Tunisia. Carrot and millet were grown during fall-winter and summer seasons on a sandy soil and surface and drip-irrigated with well water having an ECi of 3.6 dS/m. For three years, a complete randomized block design with four replicates was used to evaluate five irrigation regimes. Irrigation regimes consisted in water replacements of cumulated ETc at levels of 100% (SWB100, full irrigation), 80% (DI-80), 60% (DI-60), when the readily available water in SWB100 treatment is depleted, deficit irrigation during ripening stage (SWB100-DI60) and farmer method corresponding to irrigation practices implemented by the local farmers. The results showed that soil salinity was significantly affected by irrigation treatments. Higher soil salinity was maintained in the root zone with DI-60 and farmer irrigation treatments than full irrigation (SWB100). SWB100-DI60 and DI-80 treatments resulted also in low ECe values. Soil salinity was kept within acceptable limits for the growth of the crops grown in the rotation when SWB100, SWB100-DI60 and DI-80 strategies were employed. The rainfalls received during fall-winter and spring periods were effective in leaching salts from the soil profile. During the three year period, carrot and millet yield was highest for the SWB100 full treatment, (29.5, 28.7 and 26.8 t/ha for carrot and 27.2, 28.3 and 26.9 q/ha for millet) although no significant differences were observed with the regulated deficit irrigation treatment (SWB100-DI60). However, the DI-80 and DI-60 deficit irrigation treatments caused significant reductions in carrot and millet yields through a reduction in roots number and weight, panicle number, kernel number and weight in comparison with SWB100. The farmer’s method caused significant reductions in yield and resulted in using 43 to 57% and 27 to 47% more water, respectively, in the carrot and millet growing seasons and increased soil salinity. For all irrigation treatments, carrot yields were higher in first than the two following years and millet yield was higher in second than the first and third year. Water productivity (WP) values reflected this difference and varied, respectively, between 3.29 and 9.7 kg/m3 and 0.35 and 0.95 kg/m3 for carrot and millet crops. The lowest WP values occurred under the farmer’s method, while the highest values were obtained under DI-60 deficit irrigation treatment. SWB100 irrigation treatment provides significant advantage on yield and WP compared to farmer’s method in carrot and millet production under experimental conditions. Thus, for water-saving purposes, the SWB100 irrigation scheduling is recommended to optimize the use of saline water in carrot and millet production and to control soil salinity. Under situations of water shortage, the deficit irrigation strategies (SWB100-DI60 and DI-80) are recommended as a tool to schedule irrigation of carrot and millet crops under the arid conditions of southern Tunisia.