Typically, soil fertility has declined under continous agriculture in the tropics. Chemical fertilizers have the distinct disadvantages that they require cash and have to be transported often to remote sites. Compost only processes what organic matter the farmer already has and also must be transported from its site of manufacture to the fields.
A World Neighbors program in the lowlands of Honduras has been working with farmers to develop corn and bean production systems that incorporate green manures to maintain or improve soil fertility. Much of the research has involved testing various legume species including Canavalia ensiformis, C. gladiata, Dolichos lablab, and Mucuna pruriens. This last species, also called velvetbean, has been particularly successful.
Planted with or just after the corn, it covers the ground quickly, eliminating in many cases the need for a second weeding. After the corn has been harvested, it often climbs the old stalks, sets seed, and then dies. In many sites this allows for a natural reseeding with the corn in following years. This allows the farmer to use green manures without taking land out of food crop production.
In Honduran cornfields the velvetbean produces annually an average of 6 T/Ha of dry organic matter. Yields double that have also been recorded. Traditionally the green manures have been turned into the soil at the end of the rainy season. Workers are now testing whether turning into the soil is truly necessary. Planting directly into a dead mulch of velvetbean residue would greatly reduce labor requirements.
Velvetbean can also be used as a high quality forage for livestock. One other new exciting use is as a coffee substitute. After being roasted and ground, its acceptance as a hot beverage has created a local market for women who are presently selling over 40 lbs per week.
The flexibility of these legumes in various local production systems is a large part of the reason that around the La Ceiba and Omoa areas use of velvetbean and other green manures is spontaneously spreading.
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