Effect of nitrogen concentration in the nutritional solution and harvest time on nitrate content in baby leaf Swiss chard crop in a hydroponic system

The development of baby leaf vegetables has increased due to its fast processing operations and its attractiveness as a gourmet product. Despite these benefits, the high level of nitrates in tissues create serious health problems. To reduce these levels, monitoring dose of nitrogen fertilization and harvest time are essential. The objective of this study was to evaluate the nitrate content in two cultivars of Swiss chard (baby leaf) by modifying the nitrgen content of the nutrient solution and time of harvest. Two independent trials were performed, where the nitrate content, nitrate reductase activity (NRA) and quality parameters such as color were measured in two cultivars of Swiss chard (Beta vulgaris L. cicla) with a red (E1) and orange petiole (E2), respectively. A randomized split-plot design was performed, where the main plot corresponded to N2 dose (100, 200, 300 and 400 mg N2 L-1) and subplots of different harvest times (9, 12 and 21 h). In E1, the time of harvest was the main factor on the nitrate content, where high N2 levels were found at 8 h, and low levels at 12 and 21 h, probably due to different carbohydrate levels and reducing power available to activate the NRA, which had its maximal activity at 12 and 21 h. In E2, the content of nitrates showed a high accumulation in midrib compared to lamina. In both trials, time of harvest affected the nitrate content in lamina such that early hours should be chosen to obtain low nitrate accumulation.