This article critically explores competing knowledge claims over soil fertility in and around Kano, northern Nigeria's largest city. Drawing on methods from both the natural and social sciences, the analysis explores an apparent mismatch between local and scientific knowledge claims, and the methodological complexities of assessing soil fertility are revealed. In doing so, the paper contributes to an emerging literature which suggests that the integration of different knowledge bases is critical for understanding the complex problems of environmental sustainability. More specifically, assessments of soil fertility must not be viewed in isolation of local knowledge of environment, or livelihood diversity and change. In the case of Kano, both the environmental perceptions and soil management regimes of those living in the peri-urban interface are increasingly shaped by pressures associated with urban expansion. The article concludes that understanding soil fertility change is a complex process that must be allied to broader livelihood concerns, if sustainable environmental policies are to be initiated in the years to come.