An ongoing debate about the integration of farmers' empirical knowledge in agricultural development was sought to be answered by studying soil fertility management strategies in the Jos Plateau of Nigeria. The paper of Pasquini and Alexander (2005) tried to illustrate how farmers collectively can acquire considerable and detailed knowledge, which can be supported by scientific explanations.Since time immemorial, the idea that local people could have something to contribute to development is not always considered. Some scholars and scientists often put down local, indigenous knowledge. Often, they dismiss it as 'primitive', 'unscientific' and 'wrong'. Thus, they assigned themselves of 'educating' rural people, using a top-down, transfer-of-technology approach (Okali et al. 1994; Scoones and Thompson 1994a; Sillitoe 2002). Fortunately, Pasquini and Alexander (2005) mentioned that this perspective was challenged with a populist approach that viewed indigenous technical knowledge as a valuable, untapped source, and believed that it had to be 'incorporated' into formal research extension and practices in order to make agricultural development more sustainable.In the late 1980s-early 1990s, a thorough research in the Jos Plateau, Nigeria congruently examined how the knowledge and management of soil fertility by local farmers could be integrated in the development of a viable strategy for the maintenance of soil fertility (Phillips-Howard and Kidd 1991). As a previous site of tin mining since the beginning of the twentieth century, farming systems have been agitated about 320 km2 of cultivable land, much of which was needed for food production, because of the growing population (Alexander and Kidd 2000). In 1949, a series of trials was established to find the best way of restoring the mined land to agriculture, but after three years of trials, the Mines Land Reclamation Unit declared that it was impractical and uneconomic to raise the fertility of the degraded soil to the point that it would be able to sustain traditional arable agriculture (Alexander 1996). Local farmers were unaware of this opinion and continued with their informal reclamation strategy, which proved successful in raising significantly the nutrient status of the soils (Alexander and Kidd 2000).
Thus, Phillips-Howard and Kidd (1991) showed that farmers had extensive and detailed knowledge of a variety of traditional (in Hausa: takin gargajiya) and modern (takin zamani) fertilizers, being able to differentiate between them according to their perceived characteristics and usefulness. Inorganic fertilizers are 'modern' fertilizers, whereas various livestock manures and waste ash are classified as traditional fertilizers. In fact, the key to the reclamation strategy was that farmers applied a combination of inorganic fertilizers, different types of animal manure and urban waste ash (Alexander 1996). Also, urban waste ash was regarded as valuable by the farmers, and for this reason one of the conclusions Phillips-Howard and Kidd (1991) came to was that further investigation of the characteristics and supply of this material (tokan bola) (and other unfamiliar fertilizers such as egret manure--kashin balbela) would be worthwhile. Research carried out in the 2000/2001 dry farming season (from September through to May) aimed to provide an appreciation of the role played by urban refuse ash, while highlighting the risks attached to its use. Thus, Pasquini and Alexander (2005) have to identify