Abstract

Swiss chard (Beta vulgaris L. var. cicla) is a popular vegetable because it is nutritious, robust, easy to grow. It requires regular applications of nitrogen, which causes accumulation of oxalates and nitrates within the plant. Oxalates and nitrates are known health hazards but the use of organic fertilizers have been shown to reduce their accumulation and to promote accumulation of beneficial phytochemicals. We therefore determined the effect vermicompost (VC), Tithonia diversifolia green manure (Tithonia) and urea on the quality of Swiss chard. The experiment was laid out in a Randomised Complete Block Design (RCBD) replicated three times with thirteen treatments. Leaf nutrient elements, TSS, polyohenols, Vitamin C and antioxidants were determined using standard procedures. Treatment effects were significant only for aluminum, phosphorus and calcium. The values were highest on VC 50 kg N ha^-1 and Urea 50 kg N ha^-1, Tithonia 50 kg N ha^-1 + Urea 50 kg N ha^-1, and VC 50 kg N ha^-1, and VC 100 kg N ha^-1 for aluminum, phosphorus and calcium, respectively. Lowest response was reported on Tithonia 50 kg N ha^-1, control and Tithonia 50 kg N ha^-1 + Urea 50 kg N ha^-1 for aluminum, phosphorus and calcium, respectively. The treatments significantly influenced the percentage of polyphenols, vitamin C and the antioxidant capacity while no significance was reported for total soluble solutes. The polyphenols and vitamin C content were highest on Tithonia 100 kg N ha^-1 and control, respectively. Low polyphenol and vitamin C contents were recorded on VC 50 kg N ha^-1 and VC 100 kg N ha^-1, respectively. A similar trend was observed for antioxidant activity since a positive correlation was observed between the polyphenols and vitamin C and the antioxidant activity. Tithonia green manure improves Swiss chard quality.

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