1. Introduction Since independence, Tunisia has seen political stability. It has pursued a s- trategy of equitable devel- opment and has registered steady long-term develop- ment progress. From 1970 to 2001, real per capita in- come grew from 700$ to 2070$, while poverty de- clined from 40% to 10% for Tunisia's 2001 popula- tion of 9.7 million (World Bank, 2002). The contri- bution of agriculture to GDP was 12.5% in 2003 (INS, 2004). In the last fifty years, agricultural policy has been largely determined by considerations of food security and self-sufficiency. The irrigated area passed from 120 thousands ha in 1970 to around 400 thousands ha in 2002. Despite the irrigated area represents only 7% of the total agricultural area, the irrigat- ed sector contributes by 32% to the total agricultural pro- duction, 20% to agricultural exports and by 26% to em- ployment in agriculture (Ministry of Agriculture, Ninth Plan of Development 1997-2001). Nefzaoua Oases will continue to be important sources of date production in the South of Tunisia, contributing 45% of the total area under date production and more than 55% of total date production each year. The Nefzaoua Oases re- gion is famous for the production of high-quality Deglet Nour date. At the turn of the century, Tunisia was selling more than 20,000 metric tons in the world market which ac- counted for more than half of the total dates export of Africa or 10% of the total Tunisian agricultural export mar- ket value (FAO, 2004). Date production in Tunisian Oases has increased significantly over the past three decades, due to expansion in the irrigated area as well as massive invest- ments in irrigation development made by the government. Date production increased from 58,800 tons in 1975-1976 to 107,000 in 2001-2002. The source of irrigation in this entire region is the extracted water from the North-West Sahara Aquifer System (N- WSAS). This is one of the largest groundwater sys- tems in the world. It con- sists of two main aquifers, the Terminal Complex (TC) and the underlying Intercalary Continental (IC), and covers a total area of more than 10 6 km 2 This resource is shared by three countries: Algeria, Tunisia and Libya. The bulk of the water pumped from the system is utilized for the irrigation of approxi- mately 14,000 km 2 of agricultural land. The present situa- tion can be characterized as fossil groundwater mining, the total abstraction being 80 m 3 /s. While the stored amount of water would be able to sustain this abstraction for another 10,000 years, the water comes at a price. On one hand, there is the cost of pumping and the investment for wells and pipelines. On the other, the cones of depression created by the pumping lead to a deterioration of the water quality due to the attraction of saline waters from different sources such as the brine of the Chotts, the saline water of the underlying Turonian and the seawater of the Mediterranean. Besides the global management task for the whole basin, a number of sub-problems on a more local scale arises. For that purpose, the Nefzaoua Oases region is studied. Over the last fifty years, the pumped quantity in the Nefzaoua has increased six-fold while the irrigated area tripled. Over the last 50 years governmentally-induced expansion of irrigat- ed agriculture as well as uncoordinated growth of private farming activity have induced a considerable overexploita- tion of the fossil groundwater basins. In the vicinity of Ne- fzaoua, the change in the hydraulic regime caused local de- terioration of pumped water quality. Consequently, salinity of pumped water has risen up to 8g/l in certain areas thus rendering this water no longer suitable for irrigation pur- NEW MEDIT N. 2/2006 D ate yield and water productivity in Nefzaoua Oases of T unisia: a comparative analysis Mounir BELLOUMI*, Mohamed Salah MATOUSSI** Abstrac t The objective of this paper is to understand farm-level date yield variations, to estimate the impact of various inputs on date yields of farms, and to estimate the effects of farm-specific socioeconomic factors and environmental factors on irrigation water productivity in Nefzaoua Oases. The effect of water salin- ity on date yields is of particular interest. For this purpose data from two sam- ples of 138 Water Users Associations farmers and 134 private ones were re- spectively collected in 2002 and 2003. Analysis of results showed that water productivity of irrigation is quite low in both systems. Résumé Le but de cet article est de comprendre les variations de la productivité des palmiers dattiers au niveau de l'exploitation et d'estimer les effets des facteurs socio-économiques et environnementaux sur le rendement de l'eau dans les oasis de Nefzaoua. L'effet de la salinité de l'eau sur la productivité des palmiers dattiers est de grand intérêt. Voilà pourquoi on a collecté les don - nées à partir de deux échantillons respectivement de 138 agriculteurs des As - sociations des Usagés de l'Eau et de 134 exploitants privés en 2002 et 2003. L'analyse des résultats a montré que la productivité de l'eau d'irrigation est plutôt modeste dans les deux systèmes. 52 * Faculty of Law, Economics and Political Sciences of Sousse, Tunisia ** Faculty of Economic Sciences and Management of Tunis, Tunisia Jel classification: Q120, D240