The effect of nitrogen rates on the growth, leaf yield and nutritive quality of the black nightshade (Solanum nigrum L.)

Abstract

Two experiments were conducted between August, 1988 and March, 1989 at the Field station of the Fac~lty of Agricul t ur e , Kabete Campus, Uni versi ty of Nairobi, to study the effect of " .. nl.,-rogen (N) rates on growth, leaf yield and nutritive quality of black nightshade (Solanum nigrum L.). Four N rates (0, 5, 1~ and 15 9 per plant) in the form of Calcium Ammonium Nitrate (26%N) were used. The plant growth was assessed by the determination of plant number of leaves and bran-ches per plant, while fresh weight of edibl e portions in tons per hectare was used to assess the plant yield. The plant height, number of leaves and branches per plant increased significantly (p = 0.05 ) with increasing rates of N fertilizer. However, plants top-dressed with N higher than 5g per p Iant did not show significant increase in growth. Nitrogen rates had significant effect on fresh weight with plants that were top-dressed with 5g of N per plant giving the highest yield of 44.5 tons per hectare. The 1eaves were anal y sed for proximate chemi cal cornposition, B-carotene, ascorbic acid and six minerals including calcium and iron. B-carotene, total ash, crud e fat, crude protein, potassium, calcium and ma cn es i urn levels increased with increasing rates of ~~ application. (xiii) However ~he levels of ascorbic acid and crude fibre were significantly decreased by higher N rates. Sodium, iron and zinc contents in leaves tended not to be influenced by Nrates. The evaluation of anti-nutrient factors in leaves involved the determination of nitrate-Nitrogen (N03-N), oxalates and total phenolics. Nitrate-nitrogen in the leaves increased significantly with increasing rates of N application while the oxalate content in leaves tended to decrease with increasing N rates. Nitrogen rates had no significant effect on the total phenolic content in the leaves.