The impact of long-term irrigation on changes of ground water level and soil salinity in northern Tunisia

The irrigated area of Kalaat Landelous in northern Tunisia is an example of the successful reclamation of 3000 ha of soils affected by shallow ground water levels and salinization. Examination of soil conditions at three key periods during reclamation reveals the reasons for this success. Aspects of irrigation management define these periods, during which measurements were taken of the depth and salinity of ground water over 43 years. An overall salt balance for the irrigated areas was made in order to estimate the risk of salinization. The results reveal a lowering of the ground water level (average depth was I m and will be 1.6 m), desalinization of the soils (average electrolytic conductivity of the soil was 0.8 S m(-1) and will be 0.55 S m(-1)), and dilution of the salt content of the ground water (average electrolytic conductivity of ground water was 3 S m(-1) and will be 1.4 S m(-1)). A reduction in the variability of saline conditions was also observed. The salt balance shows a large amount of salt exported from the area, between 22,000 and 66,000 Mg, and only small areas of new salinization have appeared as a result of irrigation. Ultimately, the sustainability of the project depends upon the performance of the drainage network and on the abundance of the rainfall. If drainage is efficient, soil salinity will be maintained below wheat, corn, tomato, pepper, and alfalfa tolerance limits.