Much of sub-Saharan Africa is semi-arid and the burgeoning population depends heavily on small-scale dryland agriculture. In many areas the fertility of the farm land has fallen as the pressure of the human population has increased. A joint research project involving staff of the Kenyan Agricultural Research Institute and CSIRO's Division of Tropical Crops and Pastures was commenced in 1985. A major output of the research is a crop model which explores the interactions between water supply, nitrogen nutrition and allows appropriate adjustments to be made to planting time and plant density in accord with weather data. Proceedings of a symposium held in Nairobi, Kenya, 10-11 December 1990.