Combining Tithonia diversifolia and fertilizers for maize production in a phosphorus deficient soil in Kenya G. Nziguheba 1, * , R. Merckx 2 , C.A. Palm 3 and P. Mutuo 3 1 Department of Soil Science, University of Stellenbosch, Private bag X1, 7602 Matieland, South Africa; 2 Laboratory of Soil Biology and Soil Fertility, K.U. Leuven, Kasteelpark Arenberg 20, B3001 Heverlee, Belgium; 3 Tropical Soil Biology and Fertility Programme (TSBF), P.O. Box 30592, Nairobi, Kenya; *Author for correspondence (e-mail: gn@akad.sun.ac.za; phone: +27 21 8084790; fax: +27 21 8084791) Received 10 July 2001; accepted in revised form 13 February 2002 Key words: Economic returns, Green manuring, Maize, Phosphorus recovery, Relative agronomic effectiveness Abstract The ability of Tithonia diversifolia, fertilizers and their combination to improve maize production in a P-deficient Ferralsol was studied in western Kenya. Tithonia and fertilizers were applied separately or combined in different proportions to give equal rates of 165 kg N ha -1 , 15.5 kg P ha -1 and 155 kg K ha -1 in two consecutive maize growing seasons, followed by two residual maize crops. Maize grain yields and P recovered in the above-ground biomass were higher in the pure Tithonia than the pure fertilizer treatments. Maize yields increased with increas- ing proportions of Tithonia in the mixed treatments. When less than 36% of the P applied in the mixture was supplied by Tithonia, there was no additional yield benefit in the combined treatments compared to the pure fertilizer treatments. However an added value ranging from 18 to 24% in yield was observed at greater Tithonia proportions. Economic returns were greater when Tithonia was applied alone than when fertilizers were used, with a larger profit when Tithonia was collected from existing niches than when produced on site. Collecting Tithonia from current niches resulted also in larger net returns for all the combined treatments compared to the fertilizer treatments. The results of this study indicate that a high quality organic residue such as Tithonia can increase maize production to a greater extent than fertilizers. In low input systems, the combination of Tithonia and fertilizers is a valuable alternative when resources are scarce and an added benefit can be obtained by maxi- mizing the proportion of Tithonia in the mixture. Introduction Phosphorus is identified as one of the main limiting nutrients in smallholder cropping systems of western Kenya. The most recognized strategy for phosphorus replenishment is the use of mineral soluble P fertiliz- ers available in the market. Although farmers are aware of the increase of crop production through ap- plication of P fertilizers, the adoption of this strategy is and will continue to be constrained by their high cost, low purchasing power of smallholders and re- stricted access to credit. Addition of large amounts of P to increase capital P as suggested by Sanchez et al. (1997), also requires a large investment, implying some external interventions from either governments or other organisations. Therefore, the impact of such undertaking on smallholder agriculture should be pro- jected at a long-term. In the meantime, strategies that include the available resources need to be developed. Although organic resources such as green manure do not provide sufficient P and have no effect in in- creasing the total P of the system (Palm et al. 1997; Buresh 1999), they may increase the P availability of the already present P by rendering it more accessible to crops. The contribution of organic sources of P for crop production is limited by their low P content, thus requiring large amounts to meet moderate yield in- creases (Palm 1995). In densely populated areas such as western Kenya, large amounts of organic residues cannot be produced on small farms averaging only 165 Agroforestry Systems 55: 165–174, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.