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PRODUCTION
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Each day, 1200 naked lettuce seeds are sown with a vacuum seeder in rockwool slabs, placed in plastic trays, and moved into the growth room. For three days, the seedling trays are covered with transparent lids to maintain a high humidity around the germinating seeds. In addition, a shade screen is placed over the lids for the first 24 hours after seeding to reduce light levels during the germination process. Six days after seeding, a careful selection of the seedlings is performed and small and poorly developed seedlings are removed to ensure a uniform plant size at the time of transplant. After 12 days, the seedlings are transplanted into the greenhouse. In the greenhouse, the rockwool slabs are separated into individual seedling cells, which are snugly fitted into large washer-like plastic holders. Each holder filled with a rockwool seedling cell is then placed over holes cut in 0.6 m (2 feet) by 1.2 m (4 feet) extruded polystyrene boards (2.5 cm or 1 inch thick) which are floated on top of the nutrient solution. Initially, the plants are kept at 81 plants-m-2 (7.5 plants-ft-2) for 10 days before they are respaced to a final spacing of 28 plants-m-2 (2.6 plants-ft-2). The polystyrene boards used for the initial spacing contain 60 rectangular spaced holes with a diameter of 3.2 cm (1.25 inch). At the final spacing, each polystyrene board contains 21 rectangular spaced holes with a diameter of 3.8 cm (1.5 inch). This larger hole size allows for a more easy passage of the plant roots during the respacing procedure. The plants are grown for 14 days at the final spacing. Of the 1200 seeds sown, 12 days later 960 seedlings are manually transplanted to the greenhouse and, 22 days after seeding, 945 plants are manually respaced. The final harvest size of 150 g (5.3 ounces) is reached 36 days after seeding. Pictures of the Floating
Hydroponics Greenhouse Design:
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