Improved water control and crop management effects on lowland rice productivity in West Africa

Much of the rapidly-growing demand for rice in West Africa will be met from production in inland valley swamps which are abundant and relatively robus t with regard to cropping intensification. Rice yields in the traditional, predominating non-bunded systems are low (about 1.5 Mg ha(-1)). Informal de velopment of traditional rainfed lowlands is currently occurring across the region, mainly with low-cost interventions such as the building of field b unds. Relating lowland rice yield to quantitative information on resource b ase quality and agronomic practices will improve future research priorities and guide site and system-specific targeting of available technical option s. Diagnostic on-farm trials were conducted in 62 traditional and 40 improv ed (bunded) rainfed lowland fields in three agro-ecological zones of Cote d 'Ivoire (Guinea savanna, bimodal forest, and monomodal forest zones) to qua ntify effects of improved water control on productivity. Weed biomass and r ice grain yield were determined in farmers' fields and in super-imposed res earcher-managed subplots (clean weeding, zero N control treatment, and mine ral fertilizer N application). Grain yield variability was attributed to ag ronomic practices using multiple regression analysis. Bunding significantly increased rice grain yield across sites by about 40% and controlled weeds, with approximately 25% less weed biomass in bunded than in open plots. Min eral fertilizer N application significantly increased rice yields (18% on a verage across sites) only in bunded fields, where N use efficiency was 12 c ompared to 4 kg of rice grain per kg of applied N in open fields. Across en vironments, about 60% of the observed variability in rice grain yields was explained by water control and the timing of agronomic management intervent ions (weeding, N application). The increased development of lowland rice ar eas through the construction of field bunds has the potential to significan tly increase rice production in West Africa, while also possibly reducing l abor requirements for hand weeding and allowing for a more efficient use of mineral N fertilizers. The benefits from construction of bunds are likely to be largest in the relatively well-drained inland valleys of the savanna and bimodal rainfall forest, compared to the high-rainfall monomodal forest zones.