Purpose: Declining soil fertility is worrying in sub-Saharan Africa. Various technologies serve to mitigate or rebuild soil fertility, but uptake by farmers, especially smallholders, is low. The study addresses this adoption problem in a novel way, assessing empirically many factors from various domains (economic, socio-demographic, individual, institutional, networks and information sources) to identify what drives adoption. Design/Methodology/Approach: The panel study used data from baseline and endline surveys with 1870 smallholders in Ghana, Kenya, Mali, and Zambia. Quantitative data were analysed simultaneously via logistic regression, complemented by qualitative interviews. The study demonstrates the advantage of panel studies, as they can measure changes in practice or in farmers' attitudes. Findings: Individual factors, for example innovativeness, perception about soil fertility and correct knowledge, have the biggest influence on adoption. Socio-demographic and economic factors, by contrast, play hardly any role, as do individual information sources. Practical implications: Future research should focus on in-depth studies of individual factors, e.g. innovativeness and knowledge, and on the information environment of farmers. Communication efforts must primarily target innovative farmers, ensure high quality, address competing messages, and communicate through many different channels. Theoretical implications: The importance of 'intrinsic' factors that have previously been overlooked in adoption studies in SSA becomes clear. Originality/Value: The study is one of very few that empirically assesses a wide range of independent variables to identify the drivers of adoption. It reports not only significance but also effect sizes.