Editing Hydroponics (section)

===Continuous-flow solution culture===
[[File:Leafy Greens Hydroponics.jpg|thumb|The ''nutrient film technique'' (NFT) being used to grow various salad greens]]
In continuous-flow solution culture, the nutrient solution constantly flows past the roots. It is much easier to automate than the static solution culture because sampling and adjustments to the temperature, pH, and nutrient concentrations can be made in a large storage tank that has potential to serve thousands of plants. A popular variation is the [[nutrient film technique]] or NFT, whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated in a thin layer past a bare root mat of plants in a watertight channel, with an upper surface exposed to air. As a consequence, an abundant supply of oxygen is provided to the roots of the plants. A properly designed NFT system is based on using the right channel slope, the right flow rate, and the right channel length. The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen, and nutrients. In all other forms of production, there is a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others. NFT, because of its design, provides a system where 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 practised. 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 probably one of the more productive techniques.<ref>{{cite book |doi=10.1016/B978-0-444-63696-6.00013-X |chapter=Technical Equipment in Soilless Production Systems |title=Soilless Culture |date=2019 |last1=Van Os |first1=E.A. |last2=Gieling |first2=Th. H. |last3=Lieth |first3=J. Heinrich |pages=587–635 |isbn=978-0-444-63696-6 }}</ref>

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 are used.<ref>{{cite web|url=http://www.flairform.com/hints/nft.htm|title=Nutrient Film Technique|website=www.flairform.com|archive-url=https://web.archive.org/web/20180416110457/http://flairform.com/hints/nft.htm|archive-date=2018-04-16|access-date=Nov 22, 2018}}</ref> This allows for minor irregularities in the surface, but, even with these slopes, ponding and [[waterlogging (agriculture)|water logging]] may occur. The slope may be provided by the floor, 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 one liter per minute.{{vague|date=July 2022}}<ref>{{Cite journal|date=Oct 2014|title=What are the fundamentals of setting up an NFT system?|url=http://www.hydroponics.com.au:80/what-are-the-fundamentals-of-setting-up-an-nft-system|journal=Practical Hydroponics & Greenhouses|publisher=Casper Publications|issue=148|archive-url=https://web.archive.org/web/20170904200942/http://www.hydroponics.com.au/what-are-the-fundamentals-of-setting-up-an-nft-system|archive-date=2017-09-04|via=[[Wayback Machine]]|access-date=2017-05-16}}</ref> At planting, rates may be half this and the upper limit of 2 L/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 meters 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 meters. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and halving the flow rates through each outlet.<ref>{{Cite web |title=Dissolved Oxygen and Water {{!}} U.S. Geological Survey |url=https://www.usgs.gov/special-topics/water-science-school/science/dissolved-oxygen-and-water |access-date=2022-10-19 |website=www.usgs.gov|date=22 October 2019 }}</ref><ref name="Suryawanshi Hydroponic Cultivation"/>