Although the African nightshade is increasingly becoming an important vegetable in Kenya, the consumer demand has not been met due to its low yields occasioned by lack of fertilizer use. The general belief is that traditional vegetables are adapted to low fertility. This is despite the fact that phosphorus limits crop production in many parts of western Kenya. The objective of this study was therefore to investigate the effect of phosphorus fertilizer application rate on growth and leaf yields of three types of the African nightshade; Solanum Scabrum (SS), solanum villosum subsp villosum (SVV) and solanum villosum subsp miniatum (SVM). The treatments consisted of four rates of phosphorus (0, 20, 40 and 60 Kg P ha-1) in a factorial combination with three types of the African Nightshade, SS, SVV and SVM. To assess the effect of treatments on plant growth, eight randomly selected plants in each plot were tagged and their heights, number of leaves per plant, leaf area and leaf yields determined. The available soil P levels were also determined. There was a general increase in available soil P with increasing P rate. Similarly the plant heights, leaf numbers, leaf area and leaf yields increased with increasing P rate. The leaf yields ranged from 2.38 t ha-1 (SVM with 0 P) to 13.35 t ha-1 (SS with 60 kg P ha-1) in the first season and from 2.01 t ha-1 (SVV with 0 P) to 8.67 t ha-1 (SVM with 60 kg p ha-1) in the second season. Among the genotypes, SS had the highest leaf yields, at same P levels, followed by SVV and SVM respectively, except at the P rate of 40 kg ha-1 where the difference between SVV and SVM was not significant in the first season. However, SVM had the highest mean leaf yields in the second season followed by SS and SVV respectively. We conclude that although P fertilization was beneficial to all the genotypes, there is need to target it carefully because the response appeared to be season specific. When there is adequate rainfall, SS appears to be a good choice but under low rainfall conditions, SVM could be more attractive.
