CLIMATIC DETERMINANTS OF IRRIGATED RICE PERFORMANCE IN THE SAHEL .3. CHARACTERIZING ENVIRONMENTS BY SIMULATING CROP PHENOLOGY

Agricultural development programs in most countries of the Sahel seek to increase the intensity of irrigated rice production. Variable crop duration and temperature stresses, however, limit yields and calendrial options. In an effort to characterize climatic constraints to rice double-cropping in the region, a field-based model simulating flowering was combined with models predicting maturity and chilling- and heat-induced spikelet sterility. Simulations were performed for key sowing dates, 38 sites and three genotypes based on 10-33 years of weather records. Sowing between mid-September and mid-November was associated with near-total spikelet sterility due to chilling in all Sahelian environments. Crop duration was longest in November, increasing by 5 days per degree latitude in the continental Sahel. Greatest annual variation in duration was observed in the coastal west and extreme north of the Sahel. Climatic gradients along the courses of the Senegal and Niger rivers were associated with different annual patterns of duration and sterility. Based on the genotypes available to farmers, local rice-rice cropping calendars left little room for alternative calendars. Achieving a greater flexibility for cropping calendars would require the introduction of alternative short-duration varieties. The model permits the zonation of the Sahel in terms of calendrial options and varietal requirements. For a greater spatial resolution of such studies in the future, however, the pooling and digitalization of more weather data is recommended.