Putting weeds to work
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CTA. 1996. Putting weeds to work. Spore 65. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/47437
In eastern Africa Tithonia diversifolia, a common roadside weed with a beautiful yellow flower, may come into its own in one of the latest agroforestry systems being developed to improve soil fertility. The use of leguminous plants to increase soil...
In eastern Africa Tithonia diversifolia, a common roadside weed with a beautiful yellow flower, may come into its own in one of the latest agroforestry systems being developed to improve soil fertility. The use of leguminous plants to increase soil fertility is not a new practice but the use of nonleguminous shrubs for this purpose is less common. In western Kenya, at the International Centre for Research in Agroforestry (ICRAF) field station in Maseno, researchers have been studying the hedgerow potential of various species that grow around the farms in that area. This research has shown that two so-called hedgerow weeds, Tithonia diversifolia and Lantana camara, although not leguminous, have a relatively high percentage of nitrogen in their leaves and are ideal for mulching crops. Phosphorus is also found in surprisingly high quantities in the leaves of both shrubs. Most plant species in the same area contribute only 0.01% phosphorus, Lantana and Tithonia provide up to three times that quantity. Although not known for certain, it is thought that the roots of these plants may be associated with mycorrhizoral fungi, which form a symbiotic relationship with plants in a similar way to the root nodules in leguminous species. The fungal strands penetrate the roots in order to feed from the plants, but in return the fungus provides a greater surface area to absorb the minerals essential for the healthy growth of the host plant. Researchers began trials, first on the field station and then on farmers' fields, to find the optimum quantity of leaves that need to be applied as a mulch to the soil to achieve the optimum response. Five tonnes per/hectare of biomass was found to double, and occasionally even treble, the crop yields. However, this is a lot of dry matter to cut and the labour can be costly, particularly with the more thorny Lantana which is more widespread than Tithonia. Tithonia is only found on a third of farms in the area and ICRAF suggests that the solution for farmers is to plant Tithonia in small woodlots on degraded areas of the farm, or to intercrop the tree in the field and so reduce some of the labour costs. Amadou Niang ICRAF PO Box 30677 Nairobi KENYA