Résumé
For some years it has been observed that many rice farmers in the Senegal River valley (SRV) no longer respect the recommendations of sowing periods established by AfricaRice in the early 1990s to reduce the risks due to extreme cold and hot temperatures. Moreover, some farmers seem to get very good yields sowing out of the recommended sowing windows. A collaborative AfricaRice-SAED-CIRAD study started in 2012 within both Agence National de la Recherche (ANR) Changement Environnementaux et Socio en Afrique: Passe, Présent et Future (ESCAPE) and Climate Change, Agriculture and Food Security (CCAFS, CGIAR Research Program) projects aimed at analyzing this reality and understanding the main determinants of the shift in farmers' practices. The questions addressed included: (a) the current cropping practices and their constraints, and their possible evolution; (b) the perception of climate and its possible evolution by farmers; (c) analysis of the climate of last 30 years; (d) analysis of the consequences of climate evolution on rice development and rice cropping systems; and (e) update of the recommended sowing periods according to different rice varieties in order to minimize climate risks in the valley. The analysis of cropping practices and perceptions of climate by farmers started with 11 focus groups held throughout the SRV. The focus group was followed by individual surveys to get quantified information. An analysis of historical temperature was also started, along with modeling work (using RIDEV, Samara or Oryza) in order to assess the consequences of the climate on rice development in the SRV and to update knowledge of climate risks for different sowing dates for different rice varieties. Additional studies were also launched to verify eventual genetic drift of main cropped variety and to get data on rice behavior and phenology in farmers' fields. The main results achieved so far are presented. Focus groups indicated that farmers are very aware about climate and its recent evolution during the last decade. According to them, the rain is more important and poorly distributed in recent years, with the beginning and end of the seasons more unpredictable. It is also warmer during the hot period and colder during cold period, and the cold period has shifted and extended. Some farmers also explained reductions in yields by evolutions of both hot and cold temperatures. The shift of the cold period explains why some farmers have changed their cropping practices. However, in 2011 farmers who had sown later got bad yield because the cold arrived earlier, as it did in the past. We believe that must be related to the 2011 rainy season, which was drier than recent years but comparable to what it was in the 1990s. Detailed climate analysis is underway and will be presented at the Congress. We would like to finely characterize the evolution of temperatures and also to analyze the relationship between the rainfall amount and the cold temperatures pattern. Observations will be compared to results obtained using crop model. (Résumé d'auteur)