Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/1/2004
Publication Date: 7/20/2004
Citation: Hoque, M., Ajwa, H., Mou, B. Effect of nitrogen, phosphorus, and potassium fertilization on nutritional composition of lettuce. Hortscience. 2004. v. 39(4). p. 872. Interpretive Summary: The experiment was conducted to study lettuce yield, quality, and nutritional value in response to different levels of N, P, and K fertilizer application. Yield was increased with higher levels of N fertilizer, but was not affected by P and K application rates. The best post-harvest quality was achieved at moderate rates of P fertilizer, while higher N and P levels increased glucose content but decreased shelf life of lettuce. Romaine lettuce has much higher vitamin A, lutein, and chlorophyll content than iceberg lettuce. N fertilizer generally increased the vitamin A and lutein content of lettuce.
Technical Abstract: Lettuce (Lactuca sativa L.) is an essential salad crop for the American diet. Nitrogen (N), phosphorus (P), and potassium (K) are required for successful lettuce production and can influence lettuce quality. The objective of the study was to evaluate changes in nutritional composition of romaine (cul. Green Tower) and iceberg (cul. Sharp Shooter) lettuce in responses to N, P and K fertilization during fall production in Salinas, CA. Sixteen treatment combinations of fertilizer were selected to provide a range of treatments. N was applied at 0, 112, 225, and 338 kg/ha as ammonium nitrate; P was applied at 0, 112, and 225 kg/ha as super phosphate; and K was applied at 0 and 112 kg/ha as muriate of potash. Lutein, beta-carotene, chlorophyll a (ChlA), and chlorophyll b (ChlB) content of fresh tissue of two types of lettuce was analyzed using high performance liquid chromatography (HPLC). Yield was increased with increasing N fertilizer level, but was not affected by P or K application rates. The best post harvest quality, however, was a moderate P application rate. Increasing the N and P rates gradually increased glucose content in lettuce but decreased the shelf life. Significant differences between the two types of lettuce were found in chlorophyll, lutein and beta-carotene content. No significant correlations were found between soil fertilizer application levels and nutritional content of lettuce. However, the ratio of ChlA and ChlB were greater with the increase of fertilizer rate.