The benefits of agroforestry
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CTA. 1993. The benefits of agroforestry. Spore 43. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/45916
SOIL EROSION At ICRAF's research station in Kenya's semi arid zone, low hedgerows of Cassia siamea, a leguminous shrub from Asia, planted on the contours have led to the natural formation of micro-terraces on land sloping at 14%. The hedges take up...
SOIL EROSION At ICRAF's research station in Kenya's semi arid zone, low hedgerows of Cassia siamea, a leguminous shrub from Asia, planted on the contours have led to the natural formation of micro-terraces on land sloping at 14%. The hedges take up less space than conventional conservation structures, leaving more land available for crop production. Subsequent heavy rain proved that fields with crops alone lost a very heavy tonnage of soil per hectare compared to the small losses from fields with hedgerows. Crop yields of maize and cowpea were also significantly higher where they were grown between hedgerows than in fields with crops alone. In Rwanda ICRAF researchers have also shown that contour aligned hedgerows of trees and grasses can lead to natural terrace formation and prevention of erosion. Screening trials have identified Sesbania sesban, a nitrogen-fixing tree, as a particularly promising species. Indigenous to the region, Sesbania grows quickly producing fuelwood, bean stakes, small poles and animal fodder in less than a year. Researchers have found ways of growing and then transplanting Sesbania as young bare-rooted seedlings. Results indicate that the bare-rooted seedlings of Sesbania sesban grow and survive nearly as well as seed lings produced in nurseries in polythene bags for transplanting. SOIL FERTILITY ICRAF is conducting improved fallow trials in collaboration with national programmes in Zambia and Cameroon. The system is based on planting fast-growing leguminous trees in rotation with food crops. During the fallow period, the trees capture atmospheric nitrogen and return this and other nutrients to the soil, primarily through leaf fall. At the end of the fallow period, the farmer harvests wood from the trees and returns all leafy material to the soil as nitrogen-rich mulch. In Southern Africa, after tree fallows of only one year, maize grain yields were as much as double the yields from control plots and 60% higher than yields from plots with chemical fertilizers. The benefits are due not only to the capture and recycling of nutrients, but also to the improved physical properties of soil resulting from tree root penetration. Even higher yields are obtained, over a period of several years, from plots where mulch is combined with fertilizer applied at half the recommended rate. ICRAF PO Box 30677 Nairobi KENYA