The growing season in the semi-arid region of West Africa is drought prone and of irregular duration. Two experiments were conducted in 1986 and 1987 to test the effects of flat cultivation and tied ridge cultivation (TRC) on the yields of maize and the component crops of a maize and cowpea relay cropping system. The two research sites, with slopes of 0.05% and 3%, were near Sapu, The Gambia, on an Aridic Kandiustalf in the 700 mm rainfall zone.
Both growing seasons had above average rainfall. In both years, maize on level sites showed no response to tillage practices. On the sloped site in 1987, soil moisture 10 and 15 days after the last rain was greater with TRC than with flat cultivation and yields of sole cowpea and maize were 25% and 18% greater, respectively. On the level site, TRC had no effect on residual soil moisture or grain yield. When rainfall was well distributed, tied ridging did not appear to be a viable tillage alternative for maize-based systems on flat land in central Gambia but with modest slopes, tied ridges markedly increased soil water reserves in the 0.15 to 0.60 m depth after maize harvest.