GROWTH OF CONTAINERIZED LETTUCE TRANSPLANTS SUPPLEMENTED WITH VARYING CONCENTRATIONS OF NITROGEN AND PHOSPHORUS

The objective of this study was to investigate the response of leaf and root growth of containerized transplants of two lettuce (Lactuca sativa L.) cultivars to varying concentration of nitrogen (N) and phosphorus (P) in the fertility regime. Five N and P solutions, totalling 350 ppm, including (in ppm) 32 N:318 P₂O₅ (1:10) ; 58 N:292 P₂O₅ (1:5) ; 175 N:175 P₂O₅ (1:1) ; 292 N:58 P₂O₅ (5:1) ; a water treatment supplemented, in the latter half of growing period, by 175 N:175 P₂O₅ and water only were applied over 31 days. Differences between cultivars for mean dry weights of leaf, total plant weight, and leaf area were highly significant. An extended period of root growth, greatest dry root mass, and the highest root:leaf ratios resulted from the water treatment or the nutrient solutions with high P and low N. Nutrient solutions supplemented to plants grown in water after 18 days caused an immediate reduction in the root:leaf dry weight ratio. Growth increase patterns in leaf weight, total plant weight and leaf area were associated with effects of increased N concentration on leaf weight. Nutrient solutions with high N low P resulted in highest leaf weight and lowest root mass. Increased P concentrations reduced the rate of leaf growth and promoted better development of root mass.