Résumé
The challenge of agriculture in the up-coming decades is to feed an ever-increasing population while reducing or getting rid of chemical inputs and preserving biodiversity and natural resources. In arid and semi-arid areas of the Mediterranean basin, farmers have to face this challenge, alongside multiple environmental and climatic risks. Due to low rainfall, irrigation is instrumental for agriculture and consequently for economy, in these areas. So far, irrigation has been analyzed in terms of eco-efficiency, and is commonly associated with intensification and pollution. First, this study aimed to identify, in a semi-arid irrigated area, a set of farming practices, already implemented by farmers, with agroecological potentials. We present in this communication two “virtuous” farming systems, compared to more conventional and intensive systems. Second, based on the results from 65 semi-structured interviews, a hypothetical plot with a more agroecological management style was designed. The study was carried out in the Merguellil irrigated plain in Central Tunisia, which is entirely cultivated, with a wide variety of crop types such as horticulture, fruit trees and cereals. A first farmer installed at the plot scale, a relay cropping of fava bean (Vicia faba) with pepper (Capsicum annuum) in intercropping with olive trees (Olea europaea). In this agroforestry system, the plot was further surrounded by a windbreak cereal (sorghum) belt. The farmer used old and local varieties, very resistant to pest attacks and that require low chemical inputs, resulting in lower cost of production. Seeds were saved and reused. At the farm level, crop residues (pepper, fava bean, olive tree pruning residue) and cereals were used for livestock feeding. Another farmer used manure as an organic fertilizer after a fermentation process. This practice lead to a substantial reduction of chemical nitrogen fertilizer use. In addition, he applied a water stress period at the beginning of the cycle, in order to “stimulate root growth and improve the plant's absorption capacity”. This allowed him to avoid the use of a root growth accelerator. In both cases, different types of spatial crop rotations and successions were set up with frequent fallow periods in order to restore soil fertility. However, these interesting practices coexist with other less virtuous practices. For example, most farmers continued to intensively apply pesticides and used very high quantities of chemical fertilizers. These farmers were mostly specialized in market garden and fruit trees, extremely water consuming. They generally used high yielding varieties, less resistant to pest attacks. Furthermore, the study showed that farmers usually combined agroecological practices for different purposes: i.e. income increase, soil fertility improvement, land-use optimization. All the practices mentioned above could be combined on a single plot/farm, giving a hypothetical system with a more agroecological orientation. With an adapted water and fertilization management, such a system could improve water and fertilizer efficiency and maintain soil quality. But this may not necessarily lead to better pest control or better yields. These practices remain to be evaluated, and would be adopted by farmers only if they see it as a clear interest.