Chemical Forms and Levels of Calcium in Turnip Leaves in Relation to Harvest Time and Growing Temperature

Abstract

The production of vegetables with high nutritional values is increasingly important. Maintaining a high water-soluble Ca content in leafy vegetables needs to be explored because this form of Ca is highly digestible. Therefore, we investigated the changes in Water-, 1 N NaCl-, 2% CH₃COOH-, and 5% HCl-soluble Ca in the leaves of two cultivars of turnip (Brassica napus L.) growing in the open field from September to March. In both cultivars the leaf weight per plant was highest in December, whereas the total and Water-soluble Ca contents on a fresh weight basis reached maximum levels in November; they decreased thereafter. In another experiment, potted plants were grown for 22 days, starting from November 19 in growth chambers kept at 7, 17, 27°C with a 12-hr photoperiod (PPFD 248 μmol photon·m^-2·s^-1). In both cultivars, plant growth rate and total and water-soluble Ca contents were highest when plants were grown at 17°C. From these results, we recommend that turnips should be grown at 17°C and harvested in December to maximize crop yield and their nutritional values.