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NFT continuous flow solution culture

28.08.2015

With this method the nutrient solution perpetually flows past the roots. The continuous flow solution culture is easier to automate than the static solution culture, because sampling and adjustments to the temperature and nutrient concentration can be made in large supply tanks that are designed for thousand of plants. A very popular variation is the so called “nutrient film technique”, a technique where a very shallow stream of water containing all the dissolved nutrients requiered for plant growth is re-circulated past the bare roots of the plants in a watertight channel.

NFT continuous flow solution culture

In an ideal system, the depth of the re-circulating stream should be very shallow so that the top of the thick root mat, which develops in the bottom of the channel, although moist, is in the air. As a result, an abundant supply of oxygen is provided to the roots of the plants. NFT, because of its design, provides a system wherein all three requirements for healthy plant growth can be met at the same time - provided that the simple concept of NFT is always remembered and practiced. The result of these advantages is that higher yields of high-quality produce are obtained over an extended period of cropping. A downside of NFT is that it has very little buffering against interruptions in the flow, e.g., power outages, but, overall, it is one of the more productive techniques. The same design characteristics apply to all conventional NFT systems.

While slopes along channels of 1:100 have been recommended, in practice it is difficult to build a base for channels that is sufficiently true to enable nutrient films to flow without ponding in locally depressed areas. As a consequence, it is recommended that slopes of 1:30 to 1:40 be used. This allows for minor irregularities in the surface, but, even with these slopes, ponding and water logging may occur.

The slope may be provided by the floor, or benches or racks may hold the channels and provide the required slope. Both methods are used and depend on local requirements, often determined by the site and crop requirements. As a general guide, flow rates for each gully should be 1 litre per minute. At planting, rates may be half this, and the upper limit of 2L/min appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems. Depressed growth rates of many crops have been observed when channels exceed 12 metres in length.

On rapidly growing crops, tests have indicated that, while oxygen levels remain adequate, nitrogen may be depleted over the length of the gully. As a consequence, channel length should not exceed 10–15 metres. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and reducing flow rates to 1L/min through each outlet.

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