Influence of Vermicompost on Growth, Antioxidant Content, and Nitrate Concentration of Greenhouse Grown Spinach

Vermicompost (VC) as an alternative fertilizer source may increase the ascorbic acid content of fruits and vegetables and reduce nitrate accumulation in important leafy vegetables such as spinach (Spinacia oleracea L.). Nitrates tend to accumulate in spinach leaf petioles and may possibly form carcinogenic N-nitrosamines, especially when nitrogen rates are increased under standard inorganic nutrient management plans.  Ascorbic acid has been shown to inhibit the formation of these compounds in several studies, but unfortunately, in spinach grown with an inorganic N fertilizer source, ascorbic acid content is often reduced.  Therefore, a study was conducted to determine if the use of VC (from coffee grounds) as a fertilizer source can maintain ascorbic acid content regardless of nitrate concentration of early spring greenhouse grown spinach.  VC was added to a 1:1:1 (peat, soil, and sand) media by volume (0%, 25%, 50%, 75%) in 4.5-L clay pots and seeded with ‘Bloomsdale Longstanding’ spinach.  Three plants were grown per pot with the experiment terminated at five weeks after seeding.  Ascorbic acid, nitrate, leaf area and fresh leaf weight increased in a linear manner, with 75% VC higher than 0% VC.  Ascorbic acid and nitrate content in spinach leaves were correlated (r = 0.43, P = 0.0054), and both increased linearly up to 62 mg/100 g and 6587 mg/kg, respectively, at 75% VC.  These results suggest that VC may help maintain ascorbic acid content despite nitrate accumulation in spinach, thus making it a possible alternative or addition to inorganic fertilizers for improved human nutrition.