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.