The effect of farmyard manure and calcium ammonium nitrate fertilisers on micronutrient density (iron, zinc, manganese, calcium and potassium) and seed yields of solanium villosum (black nightshade) and cleome gynandra (cat whiskers) on uetric nitisol

The overall objective of the study was to investigate the effect of farmyard manure (FYM) and calcium ammonium nitrate (CAN) and cooking on micronutrient content (iron, zinc, potassium, calcium, manganese) and seed yield in two African leafy vegetables (ALVs), Solanum villosum and Cleome gynandra in Keiyo District of the Rift Valley Province. The micronutrients were determined using the energy dispersive X-ray fluorescence (EDXRF) analysis method. Results from the study indicated that addition of various levels of fertilisers either had no effect, depressed or slightly increased the amounts of various micronutrients in the two ALVs. Edible portions of Solanum villosum were found to be richer than their Cleome gynandra counterparts in iron, manganese and potassium content.Cleome gynandra on the other hand contained more zinc and calcium than Solanum villosum. Incorporation of either FYM or CAN decreased the iron accumulation in leafy tissues of the two ALVs. Application of FYM or CAN had no significant or clear effect on the levels of zinc and potassium in both ALVs, while moderately high levels of FYM increased the levels of manganese in Cleome gynandra but showed no clear trend in Solanum villosum edible tissues. The farmer’s crop was comparable in the  measured attributes to the produce grown on soil amended with low levels of either FYM or CAN. Boiling significantly decreased the amount of micronutrients retained in edible portions of both vegetables, except formanganese where it had no effect. The FYM and CAN fertilisers significantly increased seed yields of both ALVs. In conclusion, Solanum villosum and Cleome gynandra are rich sources of iron, zinc, calcium, potassium and manganese and incorporation of various levels of FYM and CAN improved seed yields in the two ALVs, although showing no major influence on themicronutrient densities. Traditional methods of prolonged boiling to reduce the bitter antinutrients and make them palatable seriously eroded the levels of micronutrients in some instances by up to 65%.