Effect of nitrogen, potassium and calcium concentrations on growth, yield and nutritional quality of green oak lettuce

Abstract

Plant production with adaptation of nutrient application rates may provide benefits to consumers, giving improved nutritional benefits and food functionality. This research studied the effect of nitrogen (N) potassium (K) and calcium (Ca) levels on yields and nutritional quality of green oak lettuce. Plants were grown in a NFT hydroponics system and supplied with nutrient solutions containing different levels of nitrogen (7.5, 15.0 and 22.5 mM L-1), potassium (3.0, 6.0 and 9.0 mM L-1) and calcium (2.5, 5.0 and 7.5 mM L-1). At the harvest stage (four weeks after starting treatment), plant growth and yield for plant height, number of leaves plant-1, total fresh weight, total dry weight and leaf area were recorded. The nutritional quality in terms of nutrient concentration (N, P and K), Vitamin C, total carotenoids, total chlorophyll content, phenolic content, and total soluble solids were determined. The result showed that plant growth varied, due to the different concentrations of nitrogen, potassium, and calcium. For the nitrogen treatments, plants supplied with nitrogen at 15.0 mM L-1 had the highest number of leaves plant-1. Plants supplied with nitrogen at 22.5 mM L-1 recorded the lowest of leaf area. For the potassium treatments, the total fresh weight and leaf area were highest when the plants were supplied with potassium at 6.0 mM L-1 compared to plants supplied with potassium at 3.0 and 9.0 mM L-1. For the calcium treatments, the highest number of leaves plant-1 and plant width was when plants were supplied with calcium at 5.0 mM L-1. The results on nutritional quality i.e., Vitamin C, total chlorophyll, plant mineral (NPK), total carotenoids, phenolic content and total soluble solids are discussed.