Effect of nitrogen levels and harvest timing on growth, yield and quality of lettuce under floating hydroponic system

Nitrogen (N) supply and harvest timing through 'reaping and re-growth' method are critical determinants of yield and quality in hydroponically grown leafy vegetables. Lettuce (Lactuca sativa L.) was chosen as a test crop for evaluating the effect of nitrogen applications and harvesting times. In India, farmers often apply N without guidance and improperly harvest leafy vegetables. Therefore, it is essential to determine the optimum N supply and harvesting time for yield and quality enhancement of hydroponically grown lettuce. We studied the effect of different levels of N (4, 6, 8 and 10 mmolL−1) and two harvest timings on the growth attributes and quality of lettuce. The higher N levels (10 and 8 mmolL−1) showed pronounced positive effects on growth, yield, and quality of lettuce. However, the dry matter yield and ascorbic acid content decreased with the increase in N levels. For a continuous supply of fresh cut leaves of lettuce and to optimize leaf nitrate content, the plants has to be harvested by adapting cut and come again method during winter season. The average growth rate, showed significant positive response to N. The present study demonstrates that optimum levels of N (10 mmolL−1) and harvest through cutting (after 45 days of harvesting) significantly increase the leaf yield and quality of the lettuce.