TRENDS IN FOOD CROP YIELDS UNDER DEMOGRAPHIC PRESSURE IN SUB-SAHARAN AFRICA - THE CASE OF CASSAVA IN SOUTHEAST NIGERIA

Research in 1973 attributed large cassava root yield differences among three villages in southeast Nigeria to equally large population densi ty differences. In 1993, the Nigerian national team of the Collaborati ve Study of Cassava in Africa (COSCA) went back to the three villages to see whether population growth had led to yield declines. They found that the wide gap in yields between the high and low population densi ty villages was maintained, apparently due to differences in soil type , fallow periods, cassava plant densities and harvest dates. Cassava r oot yield had doubled in the high population density area, increased b ut not doubled in the medium population density area and declined in t he low population density area, The differences in the yield trends am ong the three villages were due to the use of improved cassava varieti es in the high population density area.