In farmed parts of su-saharan Africa where population pressure is high, soil fertility has been declining as fallows become shorter and cropping gets more intense. Loss of nutrients from the soil is now a fundamental problem for farmers in eastern and southern Africa. Scientists are studying on-farm as well as on-station experimentation in western Kenya and eastern Zambia in order to find ways of retaining and restoring soil fertility so that the land can continue to supply farmers with food and livelihood. This article presents the trials being conducted in these areas.