Greenhouse Production Systems
Hydroponic Systems
Nutrient Film Technique
The nutrient film technique (NFT) is a type of hydroponic culture system in which plant roots are suspended in a thin film or recirculating nutrient solution in shallow channels (also known as gullies, troughs, or gutters) (Figure 15.2). Normally, the channels are positioned on a slope so that the nutrient solution can be fed at one end and drained, collected in a return pipe at the opposite end, and returned to the reservoir tank. The only solid media used in the system is the small piece of media in which the seed was sown to start the plant, which is necessary to keep the seed from floating away during the early stages of plant growth.
Crops Suitable for the NFT Technique
Crops suitable for use in NFT systems are raised in small pots or plugs, in rockwool cubes, or foam cubes and are placed in the channels when a substantial root system has formed. It is important that the propagation unit not contribute peat moss or other loose substances that will plug the system. After 2 to 3 weeks, the plants are transplanted into the NFT system, which usually consists of several parallel channels.
Channel Design
Care needs to be given to proper channel slope and return system to the sump tank. Channels are on a slope of 1.2 to 3.0 percent, and nutrient solution is applied at the elevated end so that the solution flows down through the channels, keeping the roots completely wet. The base of the channel must be flat and not curved to maintain a shallow stream of liquid. Often, running down the middle of the channel is a small V-shaped channel so that the solution will run along the center of the channel. The other aspect of shape is the width of the channel.
Flow Rates
The solution is discharged from the headers into the channels. The solution flows by gravity down the channels and is drained at the lower end to a large catchment pipe, which conducts the solution back to the reservoir tank. As a general guide, flow rates for each channel should be 15.8 gallons per hour (GPH) (1 L/min). Lower water flow rates are recommended for crops such as lettuce, and higher rates are recommended for fruiting vegetables.
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