Accumulation of mineral elements in five tropical leafy vegetables as influenced by nitrogen fertilization and age

The edible portions of 5 tropical leafy vegetables, Amaranthus caudatus (A), Cucurbita pepo (C), Telfairia occidentalis (T), Solanum aethiopicum (Sa) and Solanum macrocarpon (Sm), were analysed for their contents of calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), sodium (Na), zinc (Zn), iron (Fe), manganese (Mn), copper (Cu) and chloride (Cl). The analyses were performed in relation to 4 levels of nitrogen (N) fertilization (0, 100, 150 or 200 kg N/ha) and 4 harvest (H) periods (7, 9, 11 or 13 weeks post-planting).N application had no significant effect on the accumulation of Ca, K, Na, Cu and Zn in all the 5 vegetables and on the P and Mg of T, Sa and Sm. However, it depressed the Fe content of all the vegetables and the Mg content of A and C, but increased the Mn and Cl contents of all the vegetables and the P content of A and C. With increasing age, the P, Na, Zn and Mn contents of the vegetables increased significantly, while Fe and Cu of all the vegetables, the K of A, C and Sm, and P of A and T decreased.