Koh, E., Charoenprasert, S., and A. E. Mitchell. Mar 6, 2012. Effect of Organic and Conventional Cropping Systems on Ascorbic Acid, Vitamin C, Flavonoids, Nitrate, and Oxalate in 27 Varieties of Spinach (Spinacia oleracea L.). Journal of Agricultural and Food Chemistry [DOI: /10.1021/jf300051]; 60, 3144−3150.