Résumé
Vegetable crops production in the southern Mediterranean is facing two major challenges: i) producing high quantities of products in a context of climate change; ii) reducing the environmental impacts, result of intensive fertigation strategies often promoted by public policies. The objectives of this study were first to assess the fertigation strategies implemented by farmers to grow chili-pepper, in the Merguellil downstream plain, a highly crop-diversified irrigated area of Central Tunisia, then to investigate alternative and more efficient fertigation scenarios. Different methods of data acquisition (surveys, field monitoring, direct observation, laboratory analyses) were used, to collect management data for eleven chili-pepper fields (selected based on local diversity of management rules). The Optirrig crop model was used to represent the fertigation strategies and the resulting hydroagronomical processes (e.g. water drainage, nitrate leaching, crop growth, water and nitrogen stress). An automatic fertigation strategies optimization process was performed to achieve two typical contradictory objectives: increased yields and reduced water and nitrogen losses. The investigations revealed that several fertigation strategies are implemented, almost all relying on the use of high amounts of water and resulting in massive drainage and nitrate leaching. However, in some cases, farmers were able to achieve high productivity with relatively low amount of resource. By performing the automatic optimization process, an improved design of fertigation strategies (frequency, doses) in coherence with soil properties was found to be relevant to simultaneously improve yields (by 1 to 4 T.ha-1, depending on fields) and drastically reduce losses (water, nitrogen).