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Irrigation programmes are usually based on technical and economic considerations without substantial involvement of the target farmers. This study aimed to investigate farmers' discourse, practices and perceptions, and to emphasize progress, limit and synergy of farmers' representation in the modernization programme undertaken by engineers in the Fatnassa oasis in southern Tunisia. Analyses of constraints were based on the modernization programmes and on farmers' interviews. Causal relationships were represented separately as problem trees according to farmers' and engineers' perceptions. The technical solutions implemented by engineers did not achieve the expected enhancement because they disregarded inappropriate community management of the oasian system. Farmers were aware of constraints related to waterlogging and hot irrigation water since they can link causes and effects. The low frequency of delivery water turns was cited as the main constraint in spite of the fact that the farmers were themselves accountable for some inefficient irrigation practices and continuous extension of date palm plantation. Farmers failed to mention soil degradation and salinity, which were only perceived indirectly, or because they applied corrective measures. This case study allowed a critical reflection on the limitations of each approach and for the combination of experts and farmers' knowledge. Copyright agriculteurs sont eux-mêmes responsables de la faible efficience des irrigations et de l'extension continue des plantations de palmier-dattiers. Les agriculteurs n'ont pas mentionné la dégradation des sols, indirectement perçue ou parce qu'ils appliquent des mesures correctives. Cette étude de cas soutient une réflexion critique sur les limitations de chaque approche, et les avantages d'une combinaison des connaissances des experts et des agriculteurs.

Community-managed irrigation systems are commonly faced with problems of low system-level performance. A comprehensive survey was undertaken to assess and quantify the causes of the low irrigation performance in a community-managed oasis in southern Tunisia. At the irrigation system level, results showed that irrigation intervals were double those that had been expected (19-21 days). The main cause was inappropriate farmers' practices at field level where the irrigation duration was almost twice the expected 10 h ha -1. The extension of date palm plantation and technical dysfunctions played a less important role as they were counterbalanced by cancellation of irrigation in some plots. At the field scale, excessively long irrigation duration resulted from the joint effects of small fields, poor maintenance of field-level water delivery systems, uncontrolled night irrigation events and low farmer commitment. This situation emphasizes the question of efficiency and sustainability of irrigation systems when farmers subvert collective rules. Further, the situation raises the question of equity among farmers which hinders their support for the water users' association and the strict application of water allocation rules. These findings should help identify an appropriate approach and lead to positive changes in the management of community irrigation systems.

The publications in this series cover a wide range of subjects-from computer modeling to experience with water user associations-and vary in content from directly applicable research to more basic studies, on which applied work ultimately depends. Some research reports are narrowly focused, analytical and detailed empirical studies; others are wide-ranging and synthetic overviews of generic problems.Although most of the reports are published by IWMI staff and their collaborators, we welcome contributions from others. Each report is reviewed internally by IWMI staff, and by external reviewers. The reports are published and distributed both in hard copy and electronically (www.iwmi.org) and where possible all data and analyses will be available as separate downloadable files. Reports may be copied freely and cited with due acknowledgment. About IWMIIWMI's mission is to provide evidence-based solutions to sustainably manage water and land resources for food security, people's livelihoods and the environment. IWMI works in partnership with governments, civil society and the private sector to develop scalable agricultural water management solutions that have a tangible impact on poverty reduction, food security and ecosystem health. Copyright © 2014, by IWMI. All rights reserved. IWMI encourages the use of its material provided that the organization is acknowledged and kept informed in all such instances.Front cover photograph shows individual pumps in action, with the rule that only one should be operating at the same time (photo: Wafa Ghazouani). AcknowledgementsThe authors would like to sincerely thank all the farmers in the al-Bayda Canal command area for providing information and responding to questions.

Salinity problems induced by irrigation are often presented in the literature as a threat that can only be managed at the irrigation scheme scale by installing subsurface drainage. On the other hand, salinity is a constraint that has often been successfully managed locally by farmers adapting their practices. However, the continuing expansion of irrigation with related water scarcity problems plus the increasing use of groundwater of marginal quality has resulted in a new challenge that is difficult to handle at the farm level only. To assess the dynamics of soil salinity and water quality together with farmers' salinity management practices, we adapted a common approach to analyze two contrasted salinity patterns: a traditional salinity pattern in an oasis (Fatnassa, Tunisia), and a recent sodicity pattern in a large irrigation scheme (Lower Chelif, Algeria). This approach which combines surveys on farmers' perceptions and practices and salinity measurements and geochemical analysis paves the way for more integrated management of salinity problems related to water scarcity. Copyright # 2009 John Wiley & Sons, Ltd. un processus de sodisation (plaine du Bas-Chelif, Algérie). L'utilisation de cette approche qui combine des enquêtes sur les perceptions et les pratiques des agriculteurs, des mesures de salinité et des analyzes géochimiques ouvre des perspectives pour une vision et une gestion plus intégrée des problèmes de salinité liés à la pénurie d'eau.

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