Soil acidity is one property associated with decline of most crop productivity. Alfisols and Ultisols are some of the acidic soils predominant in western Kenya. An experiment was conducted in both soils to find out the effect of farmyard manure (FYM) and inorganic fertilizers on maize yield on farmers' fields during wet and dry seasons of 2006. The experiment, laid out in a randomized complete block design (RCBD), had five replications in each soil type. The treatments were: farmer's practice, N (60 kg ha ). During wet season, all treatments in Alfisols gave nearly double grain yield compared to Ultisols. In both soils, during the same season, except for optimal fertilizer, FYM was not significantly (P≤0.05) different from other inorganic fertilizer treatments on plant population, height, cob number, stover, grain yield and 100-seed weight. FYM had a 108% and 103% grain yield advantage over farmer's treatment in Alfisols and Ultisols, respectively. During dry season, plant population, number of cobs and grain yield were higher in Ultisols compared to Alfisols. In each soil type, FYM plus 30 kg N ha -1 provided maize grain yield equivalent to that of N, NP and NPK treatments. FYM had a 4% grain yield advantage over optimal and NPK treatments on Ultisols during dry season. We conclude that larger amount of fertilizers or liming is needed on Ultisols to enhance their productivity to the level of Alfisols and that due to the fact that smallholder farmers are not likely to afford large amount of fertilizer and liming, use of FYM is their best bet for maize production on both Alfisols and Ultisols as there is no significant yield advantage from N, NP or NPK over FYM. Ultisols appear to be more responsive to FYM during dry season probably due to prevailing higher temperatures and relatively dry soil which enhances faster mineralization of organic matter to available plant nutrients. Addition of N fertilizer failed to increase yield in Ultisols, probably due to decline in soil pH and consequently inefficient utilization of applied resources.

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Smallholder maize (Zea mays L.) farmers cannot cope with the high and ever increasing prices of fertilizers, resulting in continuous low grain yield, chronic food shortage and insecurity. Cheaper, sustainable alternatives of improving soil fertility are being sought. The influence of Tithonia diversifolia (Hemsley) A. Gray and fertilizer application on maize yield was studied on N and Pdeficient Alfisols and Ultisols in western Kenya. An on-farm trial, consisting of six treatments: farmer's practice, N (60 kg ha -1 ), NP (60 kg ha -1 of each), NPK (60 kg ha -1 of each N and P; K 40 kg ha -1 ), tithonia+30 kg N ha -1 , and optimal fertilizer (N, 200; P, 60; K, 120; Mg, 20; B, 5 kg ha -1 ), arranged in a Randomized Complete Block Design, with five replications in each soil type was set-up during wet and dry seasons of 2006. During the wet season, Alfisols gave about 80% more grain yield compared to Ultisols. Treatment comparison within Alfisols indicated that tithonia had a 102% yield advantage over farmer's practice; but optimal fertilizer, NPK, NP and N had yield advantage of 56%, 6%, 4% and 4%, respectively, over tithonia. Apart from optimal treatment, all other fertilizer treatments were not significantly different (P‹0.05) on grain yield. Within Ultisols, tithonia had a 96% grain yield advantage over farmer's practice; treatments optimal fertilizer, NPK, NP and N had yield advantage of 76%, 25%, 10% and 7%, respectively, over tithonia. Again NP and N were not significantly different (P‹0.05) from tithonia on grain yield. During the dry season, Ultisols gave 17% more grain yield than Alfisols. Comparison within Alfisols indicated that tithonia had a yield advantage of 30%, 30%, and 13% over N, NP and NPK, respectively. However, optimal treatment had a 4% yield advantage over tithonia. Within Ultisols, tithonia gave higher yields compared to N, NP, NPK, and optimal fertilizer in the tune of 36%, 18%, 7%, and 7%, respectively. This study concludes that use of tithonia not only enhances productivity on acidic soils, but also has a higher cost benefit compared to commercial fertilizers. However, there is need to devise methods of biomass accumulation and safe storage to enable farmers access sufficient amounts for application at sowing time.

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