## ABSTRACT

There exists widespread agreement on the need to raise agricultural productivity in West Africa. Yields are well below their theoretical potential and attainable levels (Pingali and Heisey 1999; van Ittersum et al. 2013) and a combination of adequate technologies and policies are needed to enhance production (Ruben et al. 2001, 2007). There equally exists a clear understanding that past blanket interventions have been largely unsuccessful due to the lack of incorporating heterogeneity (IAASTD 2009). Heterogeneity exists at multiple levels: at the country level, implying comparative advantages between countries and regions, but also at the smallest field level. Such withinfarm variability in soil fertility, or the variability between farms within a small geographic area, is sometimes greater than the mean variation across districts (Poulton et al. 2006; Brouwer cited in Poulton et al. 2006). As a result, responses to new technologies and fertilizer differ across fields, with the least fertile fields often being unresponsive. Some recent studies suggests that the poorest households more frequently own such fields (Marenya and Barrett 2007). For them, use of fertilizer or other inputs, such as labor for timely crop management, remain economically unattrac tive under current conditions (Tittonell and Giller 2013).