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Farmer perceptions of the Biosphysical constraints to rice production in sub-Saharen Africa, and potential impact of research

water-or nutrient-limited production levels in a given rice environment. Yield-reducing factors induce yield losses by reducing or hampering growth, including abiotic and biotic factors. Biotic factors include weeds, pests and diseases; abiotic factors include salinity, alkalinity and iron toxicity. Attainable yield (Ya) refers to the yield that can be achieved with best management practices that control yield-limiting and yield-reducing factors in a economically optimal manner. Under irrigated conditions, this is typically about 80% of Yp. The yield gap is commonly defined as the difference between Yp or Ya and actual average farmers' yields. A range of socioeconomic reasons underpin these yield gaps at harvest and the substantial losses that often occur after harvest (see Rickman et al., Chapter 27, this volume), such as lack of availability of key inputs (labour, fertilizer, etc.) and sub-optimal knowledge of improved management practices. In this chapter, we quantify farmer perceptions of major biotic and abiotic constraints that limit and reduce rice yields in farmers' fields in SSA. We also estimate the potential impact of research addressing such constraints.