Effect of Nitrogen Fertilizer on Micronutrients, Antinutrients and Toxic Substances in <i>Vernonia amygdalina</i> (Bitter leaf)

Abstract

Pot experiments were conducted to study the effect of soil nitrogen levels on the antinutrient (oxalate), toxic substances (cyanide and nitrate) and some micronutrients (vitamin C, â-carotene) and mineral elements (Na, K, Mg, Ca, Zn, Fe,and Cu) in Vernonia amygdalina. Leaves of the vegetable were harvested at market maturity and flowering for chemical analysis. Results obtained showed that the applied nitrogen fertilizer significantly (p < 0.05) increased the nitrate content of the vegetable irrespective of the stage of development with mean values of 891.00 ± 72.00 mg/kg at market maturity and 4246.00 ± 170.00 mg/kg at flowering. Cyanide and oxalate contents were not significantly (p > 0.05) affected by the applied
nitrogen fertilizer at both stages of development. The level of â-carotene was significantly (p < 0.05) elevated at market maturity with mean value of 14318.00 ± 427.00ìg/100g. The concentration of vitamin C was significantly reduced (p <0.05) at market maturity with mean value of 12.08 ± 0.62mg/100g. The level of Mg was increased significantly (p<0.05) at market maturity with mean value of 20.53 ± 0.29mg/kg while K level decreased significantly (p < 0.05) at flowering with mean value of 108.90 ± 8.30mg/kg.

Keywords: Vernonia amygdalina, nitrogen fertilizer, antinutrients, toxic substances, micronutrients