Growth and nutritional values of Chinese Kale grown in the nutrient solution with different nitrogen and potassium concentrations

Vegetables are the major sources of minerals and vitamins which are essential human nutrients. Growing vegetables in the nutrient solution of the hydroponic technique allows the easy way to control nutrient uptake by plant roots. As a result of this technique, the better yield and quality in terms of increasing the nutritional values and antioxidant compounds can be achieved. At present, hydroponically grown leafy-vegetables are popular among Thai consumers. However, the understanding of the effect of essential plant minerals on the nutritional values of Thai leafy vegetables is still limited. Therefore, two experiments in completely randomized design were conducted at the Kasetsart University, Nakhon Pathom [Thailand] to investigate the effects of N and K concentrations on growth and nutritional values of Chinese Kale grown hydroponically using the Dynamic Root Floating Technique (DRFT) during June and July 2008. In experiment 1, Chinese Kale was grown in the modified Enshi's nutrient solution with 150, 225 and 300 mg N/l and in experiment 2, was grown in the solutions with 150, 250 and 350 mg K/l. The results showed that the plant fresh-weight (g/plant), leaf number, leaf area (cm2-), chlorophyll and 6 contents (mg/100 g FW), and nitrate (NO3) content (mg/100g FW) but the vitamin C content (mg/100g FW) was decreased as N concentrations in the solution increased. This is because of vegetative growth was stimulated when plant received higher nitrogen concentration and less glucose molecules remained for vitamin C synthesis. It was found that the K concentration of 250 mg/l gave the highest plant fresh and dry weight. However, K concentrations had no effect on leaf number, leaf area, vitamin C, carotenoid, chlorophyll a and b contents and nitrate content. Therefore, if concerning the safety and quality for consumption, Chinese Kale should be hydroponically grown in the nutrient solution with 150 mg N/l and 250 mg K/l.