Farmers may control some of the many factors determining the growth and the yield of a crop. The actual decisions for crop fertilization, crop management and selection of crop varieties result from accurate decision-making rules and farming strategies which have been refined through the long-term experience of rural communities. The main objective of most small-scale traditional farmers in sub-Saharan Africa is the maintenance of the welfare of their families (and food security). Once this goal is achieved, they maintain, as far as affordable, the production conditions on their farms. The population is growing intensively and the non-cropped arable land is rapidly decreasing. Food supply to the burgeoning cities and rural areas is becoming an increasingly important issue in many developing African countries, if not the most important issue for the next ten years. Future food demand from this population would be met in the long term if both crop management and soil fertility of the cropped areas are improved. It is thus necessary to increase the use of actually available local plant nutrient sources and to increase the consumption of mineral fertilizers to meet this forecasted demand. This paper presents an analysis of farmers' practices for crop fertilization and soil fertility management in the humid savannahs of West Africa. Recommendations developed by rural development organizations and extension services are compared with farmers' practices. The complexity of the processes for decision making by farmers and the constraints met by these farmers in organizing plant nutrient supply to their crops are presented. Finally, the paper proposes a review of concepts about advisory service to farmers on crop fertilization and soil fertility management.