Korba is a coastal region and the main production area for strawberries, tomatoes, and peppers in Tunisia. Due to the use of saline groundwater in irrigation, soil salinization increases in the area. Farmers are therefore forced to reduce the salinity in the soil by adopting a suitable water management strategy "blended water," with the appropriate irrigation system "drip irrigation," and new farming techniques "crop combinations and crop rotations" to achieve sustainability. Based on the electrical conductivity (EC) of the groundwater (5.05 dS/m) and freshwater (1.7 dS/m), in our pilot plot, we determine that the blended water used in irrigation must contain 28.55% of groundwater with 71.45% freshwater to have a 50%strawberry yield potential because strawberry is the most salt-sensitive crop produced in the region. The strawberry-pepper's combination is a way to improve farmers' incomes with a 200% intensification rate, taking advantage of the rains and the availability of surface water during the wet season. However, the soil salinity used to increase under these crops from 1.28 dS/m in November 2018 to 3.04 dS/m of soil EC in September 2019. This is beyond the strawberry salt tolerance threshold (1 dS/m). Even after planting summer crops, tomatoes, and peppers, the rate of evolution of soil salinity exceeds 200% (~4.5 dS/m) and 122% (~3 dS/m), respectively. Therefore, the rotation becomes necessary to reduce the soil salinity and thus prepare the soil for the next planting of tomatoes, peppers, and strawberry-pepper's combination. The introduction of rainfed crops or fallow in the agricultural rotation system helped farmers to reduce soil salinity with about 56% and 67.2% for crop rotations including summer crops and the strawberry-pepper's combination, respectively, with a return period of 1 year.
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 (Yr), 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, Yr, 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 Tunisia, only 30% of mobilized water resources have salinity less than 2.34 dS/m. The objective of this work was to determine the best irrigation scheduling way when saline and desalinated waters are used. Different irrigation doses of freshwater and saline water are used: T80-20, T50-50 and T1d-1d. 80, 20 and 50 correspond to the percentages of irrigation water supplied in a day. For 1d-1d, this corresponds to irrigation one day with saline water and then the next day with desalinated water. Their effect on crops growth and on soil salinity was measured for three different saline waters (1.56, 4.68 and 7.81 dS/m). For irrigation with water salinity of 1.56 dS/m, the treatments T50-50 gives the better yield. For the 4.68 and 7.81 dS/m, a reduction in height was observed for all treatments. Also, for soil salinity at the end of the lettuce crop cycle, T50-50 is the best treatment that has given the best results at all levels.
In the irrigated area of Korba, aquifer high electrical conductivity exceeding 28 dS m‾¹ was measured. Increasing soil electrical conductivity has led to an abandonment of farms and a reduction of the area devoted to some crops, such as tomatoes, which fell from 450 to 210 ha, between 1998 and 2011. Some new practices such water blending, crop rotation and crop association have been introduced. The most important crop combination of strawberry–pepper is widespread throughout the area. The two crops were grown simultaneously in the same plots for two successive years during the first years of the project; this new combination reached 130 ha. During recent years, this combination has been maintained for only one year due to the observed yield decrease during the second year. In order to evaluate this crop combination and with the aim of understanding why farmers grow only one year of this combination, trials were conducted from July 2011 to August 2013. Soil electrical conductivity (EC) distribution and irrigation uniformity were analysed. During irrigation seasons, soil EC was 1.45 dS m‾¹ at the beginning (July 2011) and reached 3.3 and 5.52 dS m‾¹ respectively in August 2012 and August 2013. These soil EC values were high for strawberry. This explains why farmers choose rainfed crops, and salt‐tolerant crops during the second year. A survey concerning irrigation uniformity gave an acceptable figure of almost 90%. Even if the gross margin shows that it is not worthwhile to blend fresh and saline water, farmers opt for water blending. © 2020 John Wiley & Sons, Ltd.
In Diyar-Al-Hujjej irrigated area, aquifer’s over-exploitation, sea intrusion and abandonment of irrigated areas and wells were took place. A yield decrease for all crops was observed. Average aquifer water electrical conductivity (EC) jumps from 4 dS/m 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 one year to another (about 1,900,000 m3 in 2015 and only 60,000 m3 in 2018) while annual cops water requirements 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 2,000 US $/ha under salt water and reached even 8,000 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. Introduction of another more sustainable water source should be initiated (as desalination) even at private farm level.
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