In issue 57 of EDN, we described the merits of Tithonia diversifolia and Lantana camara, common weedy species in some parts of the world. These non-leguminous species were used as mulches by ICRAF researchers to increase maize yields. Leaves of both species contain up to 3 percent nitrogen. Surprisingly phosphorus also is found in high quantities in the leaves of these hedgerow weeds. Tithonia and Lantana contain up to three times the quantity of phosphorus found in many plant species. This may in part explain the significant yield response that was obtained with the mulch treatment of 5 t/ha of Tithonia.
A field of maize that produces 4 tonnes of grain per hectare accumulates 18 kg of phosphorus in the grain and stover (dried leaves and stalks). To maintain the fertility of the soil over years, phosphorus must be added to the soil as an amendment or through nutrient recycling. [It is not uncommon that soils contain phosphorous but that roots of most plants cannot extract it from the soil.] As plants like Tithonia and Lantana decompose, some of the phosphorus they contain becomes available to succeeding crops. The yield response the ICRAF scientists obtained using these mulches surpassed that obtained with the highest phosphorus-only treatment of 50 kg/ha. Uganda Environews (June 1997) reported that it is thought that the roots of Tithonia and Lantana may be associated with mycorrhizal fungi, which form a special relationship with the plants, in a similar way to the root nodules in leguminous plants. Mycorrhizal fungi are known to penetrate the feeder roots of plants and provide the plants with a supply of nutrients and trace elements that they have extracted from the soil.
Tithonia and Lantana also are considered valuable dietary supplements by farmers in Africa. Researchers documenting the use of indigenous trees and shrubs for fodder production by Kenyan farmers found that Tithonia diversifolia was one of the five most popular species on farms on the slopes of Mt. Kenya (a subhumid climate with 1300 mm mean annual rainfall). Lantana camara also was listed as one of the five most popular fodder species for areas characterized as warmer and drier with mean annual rainfall of 950 mm. Both of these species are used by Kenyan farmers for fodder and not only as supplements during the dry seasons. In the higher rainfall areas, Tithonia is grown as a hedge and is cut frequently to maintain a height of approximately 1 to 1.5 m, whereas Lantana is generally browsed in the drier zones throughout the year. However, caution should be taken with Lantana camara. Scientists in South Africa have determined L. camara can be toxic to sheep and cattle. It is also known as an aggressive invasive weed and can be difficult to eradicate once it is established. (Agroforestry Today, July-Sept. 1997)
[Ed (DRB): I heard Pedro Sanchez speak in June of 2004 about “Hunger and Soil Fertility in Africa.” Sanchez is cochair of the Hunger Task Force of the United Nations’ Millennium Project; the goal of the Hunger Task Force is to halve the number of hungry people in the world by 2015. During his talk he discussed the need of farmers to access plant nutrients at the lowest possible cost. Tithonia diversifolia (Mexican sunflower) was one of the crops he talked about, because it is such a good nutrient accumulator. Farmers cut it from hedges and use it as a green manure. However, he warned against planting it near other crops, precisely because it is so good at accumulating nutrients!]