Pot experiments were performed to determine the effect of heading (fruiting) on antinutrients (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients viz; vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Cu, Zn, Ca, Na and K) in Amaranthus cruentus grown in nitrogen and non-nitogen treated soil. The vegetable leaves were harvested at both market maturity (vegetative phase) and heading (reproductive phase) and were subjected to chemical analysis. Results obtained showed that the vitamin C, cyanide, soluble and total oxalates concentrations in the vegetable were significantly elevated (p < 0.05) during heading irrespective of soil nitrogen levels. Nitrate and β-carotene concentrations decreased significantly (p < 0.05) during heading except that the decrease in β-carotene was not significant in vegetable treated with nitrogen fertilizer. Similarly the result also showed that the Mg, Zn, Ca and K concentrations were not significantly affected with heading. However, the Fe concentration was increased, while the Cu and Na concentrations were reduced significantly (p < 0.05) with heading.The result concludes that harvesting of Amaranthus cruentus at vegetative phase generally reduce the levels of most of the plant toxins and still conserve most of the micronutrients in an amount to meet our dietary requirements.

Titrimetric analysis was used to estimate the level of oxalate in some Nigerian leafy vegetables treated in different ways in two sets of experiments. The treatments were boiling with retention of the water used for boiling, and freezing followed by boiling without retention of the water used for boiling. Results obtained showed that the former in which five different vegetables were used led to significant increases (p<0.05) in the oxalate content of the vegetable preparations. The exception was Vernonia amygdalina in which there was a significant decrease in the oxalate content after boiling. The latter in which three selected vegetables were used however led to significant decrease (p<0.05) in the level of oxalate of the vegetable preparation, a significant amount having been lost in the decanted water. Boiling and then discarding the water used for boiling vegetables provides a good means of reducing the oxalate content of leafy vegetables and consequently the associated food safety problems.

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Study was conducted in 2006 and 2007 cropping seasons at the experimental field of Federal University of Technology, Minna (9o 401N and 6o 301E), in the Southern Guinea Savanna of Nigeria to determine the effects of N fertilizer and the fruit positions on fruit and seed yield of okro. The treatment comprised factorial combination of five nitrogen levels (0, 30, 60, 90 and 120 kg/ha) and five fruit positions on a mother-plant (3, 5, 7, 9 and 10) which were replicated three times and laid in a Randomized Complete Block Design (RCBD). The results indicated that significant taller plants were recorded in the plots that received 120 kg N/ha while shorter plants were recorded in plots that received 0 N/ha in both years of the study. The higher N level of 120 kg/ha and lower fruit position of 3 significantly gave higher number of fruit yield while the yield decreased with decrease in N level and increase in fruit position on the mother-plant. Similarly, heavier fruits were recorded in lower fruit positions and higher N levels. The fruits formed at the lower position 3 and 5 produced more seeds with higher seed weight than those formed at the higher positions. The results also showed that significantly higher seed yield was recorded at N level of 120 kg/ha ?.

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