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, β‐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, β‐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 β‐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.