Figure 2. (a) Alley cropping in the highlands of western Cameroon. Note the large unpruned perennial trees. Perennials furnish green manure but they can also compete aggressively with food crops for moisture and nutrients. (b) Raised beds planted with maize, bean, and cocoyam. Intercropping is favored by peasant-farmers in Africa, but agronomists prefer monocropping because management effects are easier to interpret with a single crop.