Carotenoid pigments in kale are influenced by nitrogen concentration and form

The objective of these experiments was to investigate the effects of N rate and form on the accumulation of lutein, beta-carotene and chlorophyll pigments in the leaf tissues of kale. Winterbor, Toscano and Redbor kale cultivars were greenhouse grown using nutrient solution culture. In the first study, N treatments were 6, 13, 26, 52 and 105 mg L(-1) at a constant 1 NH4-N:3 NO3-N ratio. On a fresh weight basis, plant pigment concentrations (lutein, beta-carotene and chlorophylls) were not affected by N rate. When calculated on a dry weight basis, however, carotenoid pigments increased linearly in response to increasing N rate. In a second study, N rate was held constant at 105 mg L(-1) and N form was changed as follows: 100% NH4-N:0% NO3-N, 75% NH4-N:25% NO3-N, 50% NH4-N:50% NO3-N, 25% NH4-N:75% NO3-N and 0% NH4-N:100% NO3-N. Increasing NO3-N in nutrient solutions from 0 to 100% resulted in increases in both lutein and beta-carotene concentrations. Increases in carotenoid concentrations would be expected to increase the nutritional value of kale. Therefore N management should be considered in crop production programmes designed to increase the concentrations of nutritionally valuable carotenoids.