Greenhouse Production Systems
Hydroponic Systems
Floating Raft System
Floating raft system consists of horizontal, rectangular-shaped tanks 6 to 12 inches (15 to 30 cm) in depth holding a large volume of nutrient solution (See Figure 14.4). Plants are grown on floating polystyrene sheets on a nutrient solution where the plants are placed in the holes. The plant roots are partially or totally submerged in several inches of nutrient solution. Raft systems have traditionally use 4 × 8 feet (1.2 × 2.4 m) polystyrene sheets with thicknesses of 0.75 to 1.5 inch (1.9 to 3.8 cm). Growers may decide to cut the board into sections for easier handling and to prevent rafts from cracking when being moved.
Nutrient Solution
The nutrient solution from the beds is recirculated through a nutrient tank of 1,000 to 1,250 U.S. gallons (4,000 to 5,000 L). There the solution is aerated by an air pump, chilled with a refrigeration unit, and then pumped back to the far ends of each bed. The solution in the beds is static, with a circulation of 0.5 to 0.8 gallons per mintue (2 to 3 L/min). During the growing season, the oxygen concentration in the nutrient solution should range between 5 and 6 mg per liter.
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