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ISHS Acta Horticulturae 843: International Symposium on Soilless Culture and Hydroponics

THREE NON-CIRCULATING HYDROPONIC METHODS FOR GROWING LETTUCE

Author:   B.A. Kratky
Keywords:   Lactuca sativa, extruded polystyrene, net pot, nutrient solution, roots, tanks, water
DOI:   10.17660/ActaHortic.2009.843.6
Abstract:
Three non-circulating hydroponic methods for growing lettuce are described which do not require electricity, pumps or wicks. All of the nutrient solution is added prior to planting or transplanting. In the simplest system, lettuce is seeded in a tapered plastic net pot filled with growing medium and placed in a darkened, 4-liter plastic bottle filled with nutrient solution with the lower 3-cm-portion of the pot immersed in nutrient solution. Plants are automatically watered, because the entire growing medium in the net pot becomes moistened by capillary action. Plant growth reduces the nutrient solution level, creating an enlarging moist air space. Meanwhile, the root system expands and continues to absorb water and nutrients. Leaf and semi-head lettuce cultivars are usually harvested at about 6 to 7 weeks after seeding. A typical expansion of this concept to a commercial scale employs a 14-cm high tank lined with polyethylene sheeting which is filled with nutrient solution and covered with an expanded or extruded polystyrene sheet resting on the tank frame. Lettuce is planted or transplanted into net pots filled with growing medium and placed in holes in the cover. Lettuce seedlings are initially watered by capillary action, and later, by direct root uptake. The crop is harvested before the nutrient solution becomes exhausted. Another modification of this method is a float-support system in long rectangular raceway tanks. Lettuce is planted or transplanted into net pots placed in a sheet of extruded polystyrene. The cover initially floats on the nutrient solution, and then, comes to rest on 2 parallel plastic pipes (10 cm diam) resting on the tank floor as the nutrient solution level recedes due to plant growth. The tank is filled with water immediately prior to harvesting and floating rafts may be easily moved to a harvesting station.

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