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Production of vegetables in Nyeri County (Central Kenya) is greatly hampered by failure of farmers to use fertilizers. This is partly because of the relative high cost of the fertilizers. Tithonia green manure may provide a suitable alternative to the conventional inorganic sources of nitrogen. However, there is little information on its potential benefit especially in the growing of kales, (Brasicae oleraceace). Kales were grown on two experimental sites to compare tithonia green manure, poultry manure and other inorganic sources of nitrogen, namely calcium ammonium nitrate (CAN), urea and ammonium sulphate nitrate (ASN). The fertilizer treatments were applied in three levels of; 30 kg of N/ha, 60 kg of N/ha and unfertilized control, from inorganic and equivalent of organic sources. Except for tithonia green manure, all the other treatments were administered at the time of transplanting. The experiment was a Completely Randomized Block Design, with five treatments in three levels, replicated three times on each site, and each site being a replica. Individual plots measured 4 m x 3 m at inter-plant and inter-row spacing of 60 cm x 60 cm, respectively. The inter-plot spacing was 50 cm and inter-block spacing was 100 cm. The fresh weight of kales was compared for all the treatments as well as the control. The data collected were subjected to F-test using SPSS proprietary computer software (Version 12.00). Treatment means found to be significantly different from each other were separated by Duncan Multiple Range Test at 5% confidence level. The results indicated that tithonia green manure applied at 60 kg of N/ha or 9t/ha equivalent of dry matter, produced the highest fresh weight of kales followed by calcium ammonium nitrate applied at the same rates. The difference was significant and higher by an average of 7.65 % from the two experimental sites. Nevertheless, tithonia green manure was not easily available during the traditional planting season in the region. Further research is required to explore the possibility of applying it in mixture with poultry manure because as observed, many smallholder mixed farmers also keep poultry which could be a source of poultry manure. Undoubtly, organic fertilizers complement inorganic fertilizers. [ABSTRACT FROM AUTHOR]

Soil nutrient depletion as a result of continuous cultivation of soils without adequate addition of external inputs is a major challenge in the highlands of Kenya. An experiment was set up in Meru South District, Kenya in 2000 to investigate the effects of different soil-incorporated organic (manure, Tithonia diversifolia, Calliandra calothyrsus, Leucaena leucocephala) and mineral fertilizer inputs on maize yield, and soil chemical properties over seven seasons. On average, tithonia treatments (with or without half recommended rate of mineral fertilizer) gave the highest grain yield (5.5 and 5.4 Mg ha-1 respectively) while the control treatment gave the lowest yield (1.5 Mg ha-1). After 2 years of trial implementation, total soil carbon and nitrogen contents were improved with the application of organic residues, and manure in particular improved soil calcium content. Results of the economic analysis indicated that on average across the seven seasons, tithonia with half recommended rate of mineral fertilizer treatment recorded the highest net benefit (USD 787 ha-1) while the control recorded the lowest (USD 272 ha-1). However, returns to labor or benefit-cost ratios were in most cases not significantly improved when organic materials were used. [ABSTRACT FROM AUTHOR]