EFFECT OF PHOSPHATE FERTILIZER RATES ON GROWTH AND LEAF YIELD OF AFRICAN NIGHTSHADE (Solanum L. section solanum) GENOTYPES IN UASIN GISHU COUNTY, KENYA

Abstract

The African nightshade vegetable is in high demand in many parts of western Kenya, this demand has not been met due low yields caused by low use of fertilizer inputs in the region. Most of the soils found in Uasin Gishu County are acidic and deficient of phosphorus but there is inadequate information available on the appropriate rate of phosphorus to be used to produce optimum yields of the African nightshade. The specific objectives of this study were to evaluate the effect of phosphate fertilizer application rate on the growth, leaf yields and financial benefits of growing the three African nightshades in Uasin Gishu County. The experiment treatments consisted of three genotypes; Solanum scabrum (C1), Solanum villosum var. villosum (C2) and Solanum villosum var. miniatum (C3) and four rates of phosphorus; 0 (P0), 20 (P1), 40 (P2) and 60 (P3) kg P ha-1 arranged in a factorial combination. A randomized complete block design with three replications was used. The study was conducted for two consecutive seasons in Moiben Location, Eldoret East District. Phosphate fertilizer, as triple superphosphate was applied at planting time while top dressing with calcium ammonium nitrate (CAN) at 60 kg N ha-1 was done six weeks later. Soils were sampled prior to planting and later analyzed for available phosphorus using standard procedures. The plant height, leaf area, number of leaves, fresh and dry weight leaf yields were taken from 45 days after sowing and harvesting done at 78 and 77 days after sowing for season one and two respectively by picking all leaves and tender shoots. Leaf yields were determined by weighing the fresh weight and also the dry weight after drying them in an oven at 700C to a constant weight. A benefit-cost analysis for each treatment was done to determine their economic attractiveness. Plant height, leaf area, number of leaves and number of branches in the main stem increased significantly (p < 0.001) with the increase of phosphorus rate applied. The increase in fresh and dry leaf with increase in phosphorus rate was highly significant (p < 0.001) in the two seasons. The fresh leaf yields increased over the control by 285-346% and 84-407% in season one and two respectively. The dry leaf yields increased over the control by 162-328% and 163-362% in season one and two respectively. There was significant (p ≤ 0.05) interaction between genotype and phosphorus on leaf yields in the two seasons. Solanum villosum var. villosum had higher percentage increase over the control in the number of leaves in a plant and leaf yields in season one. It also had higher percentage increase over the control in the height, number of leaves, number of branches, leaf area and leaf yields. Solanum villosum var. villosum and Solanum villosum var. miniatum had high net benefits in season one and two respectively. It is recommended that 60 kg P ha-1 rate should be used for all the sampled genotypes in the long rains season. In the short rains season 40 kg P ha-1 should be used for Solanum villosum var. villosum and 60 kg P ha-1 for Solanum villosum var. miniatum. The best genotype for short and long rain season was Solanum villosum var. miniatum and Solanum villosum var. villosum respectively. Further work need to be done on the effect of Solanum villosum var. villosum at higher than 40 kg P ha-1 in the short rain season.