Response of Vernonia galamensis grown in the greenhouse to liquid fertilization

Abstract

To examine the nutrient and fertilization needs of Vernonia galamensis, a new oilseed crop, experiments were conducted in the greenhouse with V. galamensis subsp. galamensis var. ethiopica, and var. petitiana. In the first experiment, the plants were grown in soil‐less medium, irrigated, and fertilized daily with 7:3:7 Shefer liquid fertilizer at the rate of 0.5, 1.0, and 2.0 L m⁻³. Plants in the control group were fertilized every two weeks at a rate 36 times lower than the low treatment. In the second experiment, plants of var. ethiopica were grown under five fertilization regimes with different levels of nitrogen (N) and phosphorus (P)(7:3:7, 14:3:7, 3.5:3:7, 7:6:7, and 7:1.5:7 N:P:K, respectively), applied at a rate of 1.0 L m⁻³. In the first experiment, control plants of both varieties suffered severe stress affecting all aspects of growth. The three fertilization treatments elicited a uniform response in var. petitiana while var. ethiopica responded differentially, performing optimally under 1.0 L m³ of fertilizer. The growth parameter most stimulated in the case of var. ethiopica was production of primary branches and hence production of flowerheads, but optimal fertilization also had a positive effect on the oil and vernolic acid concentrations. In the second experiment, high N caused a small but significant decrease in biomass as well as plant senescence and drying. Plants grown under high P had slightly more biomass. Low N (3.5:3:7) or low P (7:1.5:7) resulted in fewer capitula. Time of flowering and number of branches were not significantly affected by fertilizer composition. High N caused a significant reduction in oil and vernolic acid yields. It seems that the negative effect of the high treatment in the first experiment was related to N rather than to P levels.