Use of soil amendments, including organic materials and mineral fertilizers, is highly recommended for the replenishment of soil nutrients, improved soil health and more efficient use of fertilizers in sub-Saharan Africa. Along with other constraints, underdeveloped markets are often cited as a reason for limited uptake of recommended practices. Recognizing the potential interrelationship among practices, we estimate seemingly-unrelated, multivariate probit models to identify the factors that determine use of inorganic fertilizer, other soil amendments, and practices to control erosion by smallholder farmers in Kenya. We then estimate demand for the most common soil nutrients (N and P). We find that, consistent with theory, farmers are price-responsive and remoteness depresses demand for mineral fertilizers. Knowledge and plot tenure have a strong influence on use of soil fertility management practices. Sex of household head affects use of soil fertility management practices only in maize production, and particularly in use of N and P. Decisions to use different categories of soil fertility management practices are correlated.