Adaptive management of irrigated rice in the changing environments of the Sahel

Key words: Alternate wetting and drying, Climate change adaptation, Crop growth simulation models, Genotype × environment interaction, N use efficiency, Oryza sativa L., Phenology, Sahelian irrigation schemes, Sowing date, Spikelet sterility, Temperature increase, Water productivity, Weed control. In the vulnerable environment of the Sahel with its erratic rainfall pattern, irrigated rice production is of major importance. To aid Sahelian rice farmers to sustain irrigated rice production, this study explores management options. It includes field experiments performed at two typical Sahelian sites and simulation studies using crop growth simulation models. This thesis provides evidence that it is possible to use less irrigation water while maintaining rice production, thus increasing water productivity. The effects of a temperature increase on the growing cycle and spikelet sterility of new rice varieties in interaction with different sowing dates is quantified. The simulation results show that the sowing window will be restricted and that the cultivar choice may alter; together they will remain the most important determinants of rice production in the coming decades. In Chapter 2, field experiments involving three water saving regimes using combinations of alternate wetting and drying (AWD) and flooding and a fully flooded control show that between 480 and 1060 mm of irrigation water was used in the water saving treatments compared with 800 to 1490 mm in the flooded rice treatment. Water productivity of the water-saving treatments was higher than of the flooded control, and yields ranged between 141 and 56% of the control. When weeds were controlled, crop yields obtained with a combination of AWD and flooding were comparable with those obtained in fully flooded plots receiving the same weed management. In Ndiaye, agronomic N use efficiency was smaller in the AWD treatments compared with fully flooded conditions. An irrigation regime for rice that starts as conventio