Soil erosion on Alfisols in Western Nigeria: V. The changes in physical properties and the response of crops

Erosion-induced changes in the physical characteristics of the surface soil under different soil and crop management treatments were monitored over a period of two years. These studies were conducted on field runoff plots established on natural slopes of 1, 5, 10 and 15%. The soil and crop management treatments consisted of bare-fallow, maize-maize (plowed and mulched), maize-maize (plowed), maize-cowpeas (no-till) and cowpeas-maize (plowed).Soil erosion increased the gravel content and decreased the silt and clay contents of the surface horizon. The moisture retention capacity of the surface soil decreased significantly. The infiltration rate decreased from 3.5 cm/min on all plots in February 1972 to 0.2 cm/min under bare-fallow, to 0.6 cm/min under maize-maize (mulch), to 1.5 cm/min under maize-cowpeas (no-till) and to 0.1 cm/min under maize-maize (plowed) in February 1974. Maize yields on the mulch and no-till treatments were maintained while those on plowed plots declined. Artificial soil removal resulted in significant reductions of maize and cowpea yields.