Tithonia diversifolia in western Kenya: relationship of tissue phosphorus concentration to soil phosphorus

Tithonia diversifolia, a shrub in the family Asteraceae, is widely distributed alongfarm boundaries in the humid and subhumid tropics of Africa. Green biomass of tithonia hasbeen recognized as an effective source of nutrients for lowland rice (Oryza sativa) in Asia andmore recently for maize (Zea mays) and vegetables in eastern and southern Africa. This paperreviews the potential of tithonia green biomass for soil fertility improvement based on recentresearch in western Kenya. Green leaf biomass of tithonia is high in nutrients, averaging about3.5% N, 0.37% P and 4.1% K on a dry matter basis. Boundary hedges of sole tithonia can produceabout 1 kg biomass (tender stems + leaves) m–1yr–1on a dry weight basis. Tithonia biomassdecomposes rapidly after application to soil, and incorporated biomass can be an effective sourceof N, P and K for crops. In some cases, maize yields were even higher with incorporation oftithonia biomass than with commercial mineral fertilizer at equivalent rates of N, P and K. Inaddition to providing nutrients, tithonia incorporated at 5 t dry matter ha–1can reduce P sorptionand increase soil microbial biomass. Because of high labor requirements for cutting and carryingthe biomass to fields, the use of tithonia biomass as a nutrient source is more profitable withhigh-value crops such as vegetables than with relatively low-valued maize. The transfer oftithonia biomass to fields constitutes the redistribution of nutrients within the landscape ratherthan a net input of nutrients. External inputs of nutrients would eventually be required to sustainproduction of tithonia when biomass is continually cut and transferred to agricultural land

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