he effect of slope, crop rotation and residue management on runoff and soil loss was investigated using field runoff plots of 25 m × 4 m on natural slopes of 1, 5, 10 and 15% on an Alfisol on the International Institute of Tropical Agriculture (IITA) research site near Ibadan, Nigeria. The soil and crop management treatments consisted of conventionnally plowed bare fallow, maize-maize (conventionally plowed and mulched), maize-maize (conventionally plowed), maize-cowpeas (zero-tillage), and cowpeas-maize (conventionally plowed). The effect of two contour lengths of 12.5 and 37.5 m was also investigated for the maize-cowpeas rotation.
Soil erosion under slopes of 5, 10 and 15% is severe for these soils and if not controlled can limit crop growth.

Mulching and no-till treatments had negligible runoff and soil loss. During 1973 the annual runoff losses from the 15% slope were 36, 2 and 2% of the total annual rainfall for the bare-fallow, mulched and no-till treatments, respectively. Annual soil losses during 1973 from the 15% slope were 230 t/ha from bare-fallow, 0.0 t/ha from maize-maize (mulched), 41 t/ha from maize-maize (conventional plowing), 0.1 t/ha from maize-cowpeas (no-till) and 43 t/ha from cowpeas-maize (plowed). Significant soil erosion was associated with only a few extremely intense storms. The soil loss during a single rainstorm increased exponentially with an increase in slope gradient. There was no definite relationship between contour length and runoff or soil loss.