Agroforestry systems have potential to diversify products and increase productivity for farmers. The major agroforestry systems are outlined below. A typical farmer is interested in only one or two tree products and / or service roles, and thus in only one or two of the planting systems described. Farmers know their needs best, and should be given full support in whatever systems are chosen.
Nitrogen fixing trees (NFTs) are special in their potential for agroforestry planting. Through nitrogen fixation, this critical soil nutrient is extracted from the atmosphere and converted to a form usable by plants. The trees don’t perform this process but instead this is done by symbiotic soil microorganisms which live in nodules on the trees roots. Bacteria of the genus Rhizobium inoculate leguminous NFTs, while actinomycetes (relatives of fungae) of the genus Frankia inoculate most other NFTs. The fixed nitrogen allows fast growth rates and high production of tree products. The nitrogen can also be made available to associated agricultural crops, and livestock through appropriate tree management systems.
The following dialogue covers the planting niche on farmland in which trees can be used to the farmer’s advantage. NFT genera most appropriate for these niches are briefly listed. Species selection and planting instructions depend on the particular site and on the farmers needs and ideas. It should be remembered that there are many non-NFTs that are very useful to farmers, and could also be used in the planting systems discussed.
Nitrogen Fixing Trees
– By mean annual rainfall and temperature
– Tolerant of problem soils
– By use and ecology
– Nitrogen fixing trees and shrubs for acid soils
– Agroforestry uses of nitrogen fixing trees and shrubs known to tolerate acid soils
– Nitrogen fixing trees for fodder production
– Nitrogen fixing tree and shrub species that tolerate acid soils