Trees make soil conservation pay
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CTA. 1991. Trees make soil conservation pay. Spore 34. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/45572
Trees in grass strips, trees on contoured bench terraces, trees on bank and ditch structures and trees contour-planted in hedgerows represent four ways in which trees can help to control soil erosion. They also supply fodder, fuelwood, timber and...
Trees in grass strips, trees on contoured bench terraces, trees on bank and ditch structures and trees contour-planted in hedgerows represent four ways in which trees can help to control soil erosion. They also supply fodder, fuelwood, timber and fruit, and give the farmer a return from land that has previously been unproductive. At their Machakos Research Station and elsewhere in East Africa, the International Council for Research in Agroforestry (ICRAF) is showing how tree planting can be integrated with other soil conservation measures. The familiar technique in Kenya is 'fanya juu' in which ditches are dug along contour lines and the earth thrown uphill to form a bank. ICRAF researchers planted napier grass on the bank and fruit trees in the ditch. In areas with rainfall as low as 700mm per year, mango, guava, avocado, banana and mulberry trees have grown well and have produced good yields, giving the farmer additional income. The napier grass is fed to livestock. With the conventional grass strips the researchers again used napier grass and planted timber trees such as Grevillea robusta on the uphill side and leguminous trees such as Cassia siamea on the downhill side. Grevillea can be side-pruned to produce a straight trunk for timber and the branches can be used for fuelwood. The napier grass and the Cassia siamea leaves can be used to feed livestock. Animal manure can be used to fertilize the maize crop growing between the grass and the tree strips. Alternatively leguminous trees like Leucaena leucocephala can be planted close together to form hedgerows grown along the contour. The hedgerow acts as a barrier to soil run-off and gradually a terrace builds up against the trees. The Leucaena can be pruned and fed to livestock or used to mulch and feed a nearby crop. These techniques have proved particularly good at controlling soil erosion. In a recent heavy storm 42mm of rain fell in 30 minutes. Over 34 tonnes of soil were lost per hectare on the control mot. On the protected areas the soil loss varied between 0.5t/ha to 4t/ha. ICRAF PO Box 30677 Nairobi KENYA