I have been reading hydroponic books and articles lately and have noticed that there is quite a lot of jargon used. One I particularly notice is NFT, which is occasionally defined, but much more often not. I recognise that it stands for Nutrient Film Technique, but what does that mean?
Answer by RICK DONNAN
As you state, NFT stands for Nutrient Film Technique, and as for jargon in many industries, it is often used by people assuming that everyone knows what it is.
In its basic form it is a ‘closed’, or recirculating hydroponic system using channels (often called gullies) down, which flows a film of hydroponic nutrient solution. Typically, there will be a holding tank containing the solution and a pump, which sends it to the top of the channels. The solution then flows as a film down the channel and returns by gravity into the tank.
The plants have usually been started in a small media plug and are then planted into holes in the top of the channels. These holes are placed at a distance apart to suit the final size of the plant at harvest. Most systems have automatic water make-up through the use of a float valve. Fertiliser can either be added manually or by installing an automatic controller.
The basic principle of NFT is to maintain adequate oxygen dissolved in the water flowing down the gulley. When dissolved oxygen is used up by the plant roots (for respiration) then with a thin water film oxygen can be replaced by absorption through the large water surface area.
In the 1960s, a system of this type was used as a research technique by CH de Stigter of the Plant Physiological Research Centre, The Netherlands, but it went no further.
In the 1970s. Dr Allen Cooper of the Glasshouse Crops Research Institute (GCRI), England, saw the potential of development of the technique for commercial use. Cooper coined the term Nutrient Film Technique and is generally regarded as the ‘father of NFT’. He wrote the NFT bible, titled The ABC of NFT, which is still in print and available from Casper Publications, the publisher of this magazine.
GCRI formed an NFT research group, led by Cooper, which not only researched the technique, but helped with advice to the English glasshouse growers who began to use it commercially. Many existing glasshouse tomato growers adopted the technique. All these used plastic layflats about 300mm (12 inch) wide pegged to a central wire, as gullies laid on carefully graded floors. There was one large lettuce grower on the ground also, but using narrower channels.
At the same time growers in The Netherlands were increasingly using the dripper fed rockwool systems, which had been developed in Denmark. In England, while tomatoes were successful in NFT there were problems with root death in cucumbers. This led to the use of rockwool and over the next few years gradually most NFT tomatoes changed to rockwool.
In the late 1970s and early 1980s publicity of the success of NFT at GCRI led to the installing of many new NFT systems, mainly small, scattered around the world. Notable was some 1200 installations in the USA, resulting in the very high failure rate typical of USA commercial hydroponic operations. In contrast, none were built in Holland, the world leader in commercial hydroponics, because of the perceived disease risk.
In the mid 1980s in Australia, NFT channels on tables were developed to grow lettuce. Most lettuce farms were family businesses and the tables made working much easier. Consequently, faster crop turnover and the resulting higher yield led to a large increase in the number of these units, giving Australia more area of NFT than the rest of the world combined.
There were no significant actual changes until the last 10 years with the increasing development of automated mobile NFT gully systems. Here moveable gullies are planted at one end then move through the glasshouse to be harvested at the other end.
Design and management
Failure to allow for re-oxygenation of the water in the channel will lead to plant root death and the loss of the crop, which has happened often because of poor design, such as using small round pipes.
The initial Australian gullies were 100 x 50 mm (4 x 2 inch) electrical conduit. This led to the production of specialised channel having features such as removable lids and small centre ridges to keep the initial water flow central in the channel. These are suitable for short-term crops such as lettuce, herbs and Asian greens. For channels laid as tables on support, allowance needs to be made for sage, hence I specify a minimum slope of 1 in 40 (2 ½%), plus a maximum length of 12 m.
For wide layflat on a perfectly smooth surface, Cooper recommended a minimum slope of 1 in 100 (1%).
Apart from gullies based upon supported plastic layflats and rigid channels, there have been a number of variations from these basic designs.
In the 1980s a company called Aerial developed a ‘second generation NFT’. The company was directed by Alan Cooper and Kenneth Edwards. The basis was a special dual channel having two sides in an inverted vee. Plant roots were split between the two channels and allowed the use of different solutions or to alternate flow between the two. It was heavily promoted, especially as being easy to use, which I failed to understand, and it never established.
Finland designed a ‘super NFT’, which used a wide channel with a drain running the full length of the channel. Large rockwool blocks were dripper fed with the excess running into the drain and recirculating. A similar system has recently been developed in Holland, but there is no commercial use that I know of, and I don’t consider it to really be NFT (where is the film?)
There have been versions of ‘vertical NFT’ where plants such as strawberries and shallots have been planted in the sides of round pipes inclined some 10 degrees off vertical. These have been placed on ‘A frames’ and fitted into a return pipe at the bottom. RD
For more indepth understanding get a copy of the original book written by Dr Allen Cooper. Ω