Abstract
Studies to evaluate the efficacy of Jatropha curcas L. (Jatropha) seed cake as an organic fertilizer were carried out at Bunda College of Agriculture during the 2010/2011 growing season using an on-station experiment. The major objective was to evaluate the efficacy of Jatropha seed cake as an organic fertiliser. The field experiment was laid in a 3 × 3 design with 3 levels of Jatropha (0, 92 and 184 kg N/ha corresponding to 0, 2875 and 5750 kg DM of Jatropha seed cake, respectively) and 3 levels of inorganic fertilizer (0, 23 and 46 kg N/ha). Field results showed that maize yields responded to the amount of Jatropha seed cake while inorganic fertilizer rate and the combination of Jatropha seed cake and inorganic fertilizer (at the same level of Jatropha seed cake) did not affect the grain yield of maize. The best performer in terms of grain yield was a treatment combination of 5750 kg/ha of Jatropha seed cake and 23 kg N/ha of inorganic fertilizer which produced a grain yield of 2483 kg/ha. However, this was comparable to 2331 kg/ha produced by the combination of 2785 kg/ha of Jatropha seed cake and 46 kg N/ha of inorganic fertilizer. The grain yield of sole Jatropha 5750 kg/ha was 2126 kg/ha. The grain yield of full rate of inorganic fertilizer (23:21:0+4S + urea) application was 2853 kg/ha. It can be concluded from this study that sole application of Jatropha seed cake has a potential of producing grain yield comparable to full rate inorganic fertlizer application. Key words: Jatropha seed cake, organic fertiliser, inorganic fertiliser.  
Highlights
The term soil fertility is generally defined as the quality of a soil that enables it to provide nutrients in adequate amounts and in proper balance for the growth of specified plants when other growth factors, such as light, moisture, temperature, and the physical condition of the soil, are favorable (NAL, 2015)
The best performer in terms of grain yield was a treatment combination of 5750 kg/ha of Jatropha seed cake and 23 kg N/ha of inorganic fertilizer which produced a grain yield of 2483 kg/ha. This was comparable to 2331 kg/ha produced by the combination of 2785 kg/ha of Jatropha seed cake and 46 kg N/ha of inorganic fertilizer
The grain yield of full rate of inorganic fertilizer (23:21:0+4S + urea) application was 2853 kg/ha. It can be concluded from this study that sole application of Jatropha seed cake has a potential of producing grain yield comparable to full rate inorganic fertlizer application
Summary
The term soil fertility is generally defined as the quality of a soil that enables it to provide nutrients in adequate amounts and in proper balance for the growth of specified plants when other growth factors, such as light, moisture, temperature, and the physical condition of the soil, are favorable (NAL, 2015). The inherent soil fertility decreases with an increase in soil cropping; especially when the essential nutrients taken up by crops are not replenished (Ilex EnvironSciences, 2018). Zingore et al (2015) reported that land degradation associated with poor soil fertility leading to decreasing agricultural productivity is a problem in sub-Saharan Africa (SSA) whereas Mungai.
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