In Tunisia, water used for irrigation is often saline, increasing the risk of salinization for soils and crops. In this study, an experiment was conducted on a tomato crop cultivated on a silty-clay soil irrigated with three different water qualities: 0, 3.5, and 7 dS·m⁻¹. Experimental data were then used to calibrate and validate the Hydrus-1D model, which simulates water flow and salt transfer in soils. The successfully-calibrated and validated model was then used to study the combined effects of the soil osmotic and soil matrix potentials on root water uptake. The values of the root mean square error (RMSE), the coefficient of determination (CD), the modeling efficiency (EF), and the coefficient of residual mass (CRM) were close to their optimal values for both soil water content and soil electrical conductivity profiles, indicating the reliability of the model to reproduce water and salt dynamics. Relative yields (Y_r), indirectly estimated using actual and potential root water uptake (transpiration), indicated that the multiplicative stress response model (using the S-shape model) satisfactorily simulates measured yields and reproduces the effects of irrigation with saline waters on crop yields. An alternative scenario using a reduction of water requirements by 50% was investigated to assess an irrigation method with considerable water savings. As the results show that relative yields, Y_r, were only slightly reduced, the crop water requirements estimated by CROPWAT 8.0 must have been overestimated. The variation of the soil salinity in the root zone highlighted a high salinization risk in the short-term when water of 7 dS·m⁻¹ is used for irrigation.

In arid and semi-arid regions like Tunisia, irrigation water is typically saline, posing a risk of soil and crop salinization and yield reduction. This research aims to study the combined effects of soil matric and osmotic potential stresses on tomato root water uptake. Plants were grown in pot and field experiments in loamy-clay soils and were irrigated with three different irrigation water qualities: 0, 3.5, and 7 dS/m. The Hydrus-1D model was used to simulate the combined dynamics of subsurface soil water and salts. Successful calibration and validation of the model against measured water and salt profiles enabled the examination of the combined effects of osmotic and matric potential stresses on root water uptake. Relative yields, indirectly estimated from actual and potential transpiration, indicated that the multiplicative stress response model effectively simulated the measured yields and the impact of saline water irrigation on crop yields. The experimental and modeling results provide information to aid in determining the salinity levels conducive to optimal crop growth. The findings indicate that the selected salinity levels affect tomato growth to varying degrees. Specifically, the salinity levels conducive to optimal tomato growth were between 0 and 3.5 dS/m, with a significant growth reduction above this salinity level. The gradual salinization of the root zone further evidenced this effect. The scenario considering a temperature increase of 2 °C had no significant impact on crop yields in the pot and field experiments.

Irrigation in Tunisia is threatenedall over the country. The irrigated coastal area of Dyiar-Al-Hujjej has observed a drop-in agricultural activity following a seawater intrusion. Thus, yields have become disrupted in direct relation to the quantities of fresh water supplied and transferred over a distance of 100 km. For the sustainability of this perimeter, the feasibility of using desalinated water to stabilize the irrigation water supply was analyzed. When all crops water requirements are to be met with desalinated water, the net income is negative for all crops currently grown, except strawberry. All the open-field crops remain unprofitable even in the case of agro-industrial development, except tomatoes. A blending between desalinated seawater and aquifer saltwater leads also to a negative income for the main crops. The introduction of greenhouses to replace the same open-season crops is beneficial when desalinated water is used. The use of desalinated water in irrigation faces the high cost of desalination (0.5 US $/m³) while the average price of irrigation water in Tunisia is 0.05 US $/m³. Desalination can be recommended only in the case of crops with low need for water and high added value.

In arid countries like Tunisia, the need to find new sources of water for irrigation has become imminent. Desalination of seawater can be an alternative to irrigation. In this article, we take a look at the leading food companies specializing in desalination for irrigation around the world and the prospects for the solar energy desalination potential for irrigation in Tunisia. We have noticed that several companies invest money to desalinate water for agricultural purposes. However, the cost of a cubic meter of water sometimes remains high to go forward in this new technology. Dans les pays arides comme la Tunisie, le besoin de trouver de nouvelles sources d'eau pour l'irrigation est devenu imminent. Le dessalement de l'eau de mer peut être une alternative à l'irrigation. Dans cet article, nous examinons les principales entreprises agroalimentaires spécialisées dans le dessalement pour l'irrigation dans le monde et les perspectives du potentiel de dessalement avec l'énergie solaire pour l'irrigation en Tunisie. Nous avons remarqué que plusieurs entreprises investissent de l'argent pour dessaler l'eau à des fins agricoles. Cependant, le coût d'un mètre cube d'eau reste parfois élevé pour aller de l'avant dans cette nouvelle technologie.

In Diyar-Al-Hujjej irrigated area, the aquifer’s over-exploitation, sea intrusion, and abandonment of irrigated areas and wells took place. A yield decrease for all crops was observed. Average aquifer water electrical conductivity (EC) jumps from 4 to 6.6 dS/m between 1969 and 2017. A fresh surface water transfer over more than 100 km was launched in 1998 to safeguard this irrigated area but this fresh water supply is not stable; it varies from 1 year to another (about 1,900,000 m³ in 2015 and only 60.000 m³ in 2018) while annual crop water requirement of the perimeter is about 2,500,000 m³. An adaptation by farmers to this new situation of saline and water stress was observed. The follow-up surveys of the farmer’s practices showed that (i) new crops with high added value grown during the rainy season were introduced in association with dry season crops (strawberry-pepper association), (ii) rainfed crops, fallow, and water blending are common practices; and (iii) growing of rainy season crops in the aim to reduce water supply. The instability of fresh surface water volume transferred constitutes the main threat for this perimeter. The use of aquifer salt water must be stopped; it is the cause of the large quantities of salts supplied (over 13,000 kg/ha) and also of the low annual net income achieved. Net revenue was less than 2000 US $/ha under salt water and reached even 8000 US $/ha when sufficient surface water is available. An agrarian reform policy must be applied for this perimeter; only crops whose water requirements are partially met by rain should be grown. The introduction of another more sustainable water source should be initiated (as desalination) even at the private farm level.

Daghari I, Daghari H, Ben Khalifa N,, Mahmoud M. 2022. Saline irrigation management in field conditions of a semi-arid area in Tunisia. Asian J Agric 6: 103-108. Tunisian saline soils occupy about 25% of the total irrigated area. The irrigated area of ??"Dyiar-Al-Hujjej" in Tunisia was considered because seawater intrusion took place and salinization of the aquifer reached a very high water electrical conductivity value of 15 dS/m in the 90s, which caused many local farmers to abandon land parcels and wells. In addition, salinity has reduced plant growth and water quality, leading to lower crop yields and degradation of stock water reserves. Excess salt affects overall soil health, reducing productivity. It kills plants, leaving bare soil prone to erosion. In this study, the electrical conductivity of the soil under several irrigated crops was evaluated for two soil layers (0-20 cm and 20-40 cm). Follow-up surveys of agricultural practices have shown that the irrigation water's quality has a considerable effect on the soil's electrical conductivity and, therefore, on the choice of crops. We also showed that crop rotation is a practice done by farmers to maintain and improve soil fertility by utilizing soil nutrient losses due to salinization. This study can be the basis of a valuation to allow farmers to have the best cultural practices to fight the salinization of their soils.