The influence of nitrogen application on the growth and mineral content of two African nightshade species (Solanum spp.) cultivated in Kenya
Plant growth, leaf nitrogen and nitrate-N, and chemical content of two African nightshades, Solanum villosum and S. sarrachoides under different nitrogen levels was investigated in field experiments in 2001 and 2004. Plants were supplied with 0, 1.3, 2.6 and 5.2 g N/plant. Both African nightshade species responded similarly to nitrogen supply. Leaf area and dry matter production of plants supplied with nitrogen was 4-8 times that of plants not supplied with nitrogen. Plants supplied with nitrogen had significantly higher specific leaf area but had a lower leaf to stem ratio (p≤0.05). Leaf nitrogen concentration was significantly higher (p≤0.05) in plants supplied with nitrogen. However, when expressed on a leaf area basis, the differences in the leaf nitrogen content between nitrogen treatments were minimal. Leaf blade nitrate-N tended to be high in young plants especially those that were supplied with nitrogen. The species showed significant differences (p≤0.05) in the mineral content. It was concluded that African nightshade responded to limited nitrogen by drastic reduction in leaf area to maintain the leaf nitrogen content.
Key words: Leaf nitrogen, leaf to stem ratio, mineral content, nitrates, Solanum sarrachoides, Solanum villosum