Rethinking water and crop management in the irrigated district of Diyar-Al-Hujjej (Tunisia).

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 m in 2015 and only 60.000 m in 2018) while annual crop water requirement of the perimeter is about 2,500,000 m. 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.