Effect of plant density and harvesting frequency on the yield and vegetable quality of four variants of black nightshade (Solanum nigrum L).

Abstract

Two experiments were conducted at the Field Station of the Faculty of Agriculture, Kabete campus, University of Nairobi, between August, 1990 and May, 1991; to study the effect of plant density (22,220, 33,330 and 66,660 plants/ha) and harvesting frequencies (weekly and fortnightly) on yield of black nightshade (Solanum nigrum L.) and its variants (Solanum eldorettii, Solanum pseudonigrum (serrated leaf) and Solanum pseudonigrum (smooth leaf)). The study also looked at the influence of plant age on crude protein, B-carotene, total ash, iron, calcium and fibre contents of the leaves. The experiments were carried out in split-split plot design with three replicates. Significantly higher yields were produced with high than low plant density. Weekly harvested plants produced significantly more shoots but of less weight than fortnightly harvested ones. There were significant differences between the four variants in their fresh shoot and leaf yields. Solanum pseudonigrum (smooth leaf) produced 82.6 and 48.8 tons/ha, Solanum eldorettii produced 71.9 and 42.6 tons/ha, Solanum pseudonigrum (serrated leaf) produced 61.2 and 41.6 tons/ha and Solanum nigrum produced 52.8 and 32.9 tons/ha. of fresh shoot and leaf yield, respectively, at the best treatment combination which was plant density 66,660 and fortnightly harvesting frequency. Leaf B-carotene and crude protein contents of the four variants were not significantly different. However, Solanum eldorettii had significantly higher total ash, iron and calcium contents than the other variants which were not significantly different from each other in total ash but were significantly different in iron and calcium contents. Crude fibre contents differed significantly amongst the four variants. Solanum eldorettii and Solanum nigrum gave significantly lower fibre than the other two variants. Plant age had significant effect on the fibre, Bcarotene and protein contents but not on the total ash, iron and calcium contents of the variants. Fibre contents increased significantly with plant age. The results are discussed, implications of the results are mentioned, conclusions are summarized and recommendations for future research work highlighted.