11/30/2023 0 Comments Crop king bato bucket spacingThe slope of the channels in an NFT unit need not be severe. A flow rate of 0.2 liters/min was optimum when these gullies were 3.1 m long. One experiment compared gullies between 60 and 150 mm wide and found that 80 mm wide gullies, 40 mm deep with a slope of 1.5% were best. Rectangular PVC gullies are usual for these systems. Some of these systems attempt to make better use of greenhouse space by using various vertically spaced gully systems or horizontal systems with movable gullies to permit spacing to be adjusted as the lettuce grow. Over recent years, systems have become more intensive. Other early installations used selected profiles of long run roofing steel with baked epoxy finishes. Some of the earliest systems used ordinary wide span greenhouses with concrete floors in which narrow gullies were cast for the NFT solution. Lettuce in NFT Lettuce has been grown in NFT for many years. This may be more easily heated during the winter months to obtain optimal temperatures for growth, or cooled during hot summers to avoid bolting and other undesirable plant responses. A principal advantage of this system in comparison with others is that a greatly reduced volume of nutrient solution is required. The base of the channel must be flat and not curved, because there will be a considerable depth of liquid along the center of a channel with a curved base, merely because of the shape of the base (Cooper 1996). If inadequate, it is to be expected that yields will be directly proportional to channel width. The inlet flow rate must not be so rapid that a considerable depth of water flows down the gradient The width of the channels in which the roots are confined must be adequate to avoid any damming up of the nutrient by the root mat. The key requirements in achieving a nutrient film situation are described by Cooper (1996) as being: To ensure that the gradient down which the water flows is uniform and not subject to localized depressions, not even a depression of a few millimeters. It is extremely important to maintain this basic principle of a nutrient film because it ensures the root system has access to adequate oxygen levels. The root mat develops partly in the shallow stream of recirculating solution and partly above it. With the NFT system, a thin film of nutrient solution flows through plastic channels, which contain the plant roots with no solid planting media. History The nutrient film technique (NFT) was developed during the late 1960's by Dr Allan Cooper at the Glasshouse Crops Research Institute in the U.K.
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