Alley cropping refers to the growing of crops in alleys between rows of trees or woody shrubs, those most commonly being leguminous species. The trees are fast growing, deep rooted, and if they are legumes, fix nitrogen from the atmosphere. They are able to grow through most of the dry season. The trees or shrubs are heavily pruned at the beginning of the wet season to open up the canopy for annual crops. They may be pruned several more times during the wet season. The prunings are used as a mulch (shown in the photo), which provides nutrients to the annual crops and protects the soil from the direct impact of rain

Photo courtesy of Dr. K. Molongoy, International Institute for Tropical Agriculture, Nigeria.

This system or various adaptations of it are key to modern sustainable cropping systems in the humid tropics. Previously, slash and burn systems with long fallow periods were able to sustain fertility, but with increased population pressure, fallow periods shortened and the systems were not proving to be sustainable, even with inputs of commercial fertilizers. The alley cropping systems are most beneficial on sloping lands where the trees are planted along contours, resulting in a kind of natural terracing and greatly reduced erosion.