Tropical alley cropping and improved fallows

Abstract

Alley cropping is an agroforestry practice of growing an arable crop between rows of trees or perennial shrubs. In tropical alley cropping, the perennial species, usually leguminous trees or shrubs, are planted and managed as hedgerows less than 10 m apart with the crop planted in the interspaces or alleys between the hedgerows. The trees are pruned at regular intervals during the cropping phase and the succulent biomass of leaves and twigs is added to the alleys as green manure (Temperate alley cropping, discussed in Chapter 10, is a form of intercropping between rows of trees where the trees are not pruned, and tree rows are spaced wider). The soil-improving attributes such as efficient nutrient recycling and soil-erosion control of the tree-based system create soil conditions comparable to those in the fallow phase of shifting cultivation. The choice of tree species is an important factor that determines the success or failure of the system. Improved Fallows was introduced as a new technology in the 1990s although its scientific basis is not different from that of tropical alley cropping: using fast-growing nitrogen-fixing trees and shrubs to support the growth and production of food crops growing simultaneously or sequentially with them. More than three decades of research and development experiences with these technologies have shown that they perform well under conditions of adequate water availability during crop growing seasons but are unsuitable for dry areas. Despite their technical merits, however, farmer adoption of the technologies has been low, and it is attributed to administrative failures in creating an enabling environment for providing credit and financial support, seeds and other planting materials, and strategic failures in pushing the boundaries of testing to ecological regions that are way beyond the "safe" zones for these technologies.