Lettuce (Lactuca sativa L.) is the most widely consumed leafy vegetable worldwide. In recent years, hydroponics lettuce production has increased in Florida. Despite the lower pest, disease, and weed pressure, and the reduction of water and nutrient requirements, the increasing prices of fertilizers, including phosphorus (P), present a major hurdle for hydroponic lettuce production. Identifying lettuce genotypes capable of producing high yields with low P inputs may help reduce fertilizer use, production costs, and excess P in wastewater. The objective of this study was to identify lettuce genotypes that use P more efficiently in a hydroponic system.
Two greenhouse experiments were conducted at the University of Florida/IFAS Everglades Research and Education Center in Belle Glade, FL. In each experiment, 12 lettuce genotypes: romaine (6); crisphead (5); and bibb (1) types were grown in two nutrient lm technique (NFT) systems. Each system contained a modified Howard Resh solution plus one P treatment: either low P (3.1 ppm) or high P (31 ppm). Phosphorus was supplied in the form of phosphoric acid (H3PO4), with all other macro and micronutrients kept constant. Solutions were replaced every 14 days to avoid nutrient imbalance.
Electrical conductivity and pH of solutions were adjusted to the ranges of 1.4 to 1.8 mS/cm and 6.0 and 6.5, respectively. The genotypes were replicated three times in each NFT system, with each replicate consisting of a single plant. Seedlings were started in rockwool cubes and transplanted into the NFT 11 days after sowing. Plants were harvested at horticultural maturity to measure fresh weight [FW (g)] of shoots and roots and tipburn incidence. After shoot and root tissues were oven-dried at 65 °C for 7 days to obtain dry weight [DW (g)], then the root-shoot DW ratio was calculated. Tissue total-P concentration [TTP (mg·g-1)]was measured in Experiment 1 only, following a hydrochloric acid extraction and analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES).
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Kreutz, Gustavo & Bhadha, Jehangir & Sandoya, Germán. (2022). Lettuce Cultivated in Hydroponics Responds to Less Phosphorus Inputs.