by J Benton Jones, Jr.

Nutrient Film Technique (NFT)

In the early 1970s, Allan Cooper (1972) introduced his nutrient film technique (whose acronym is NFT) that changed the basic concept of hydroponic growing since no rooting medium is required. Cooper’s NFT presentation at the Hydroponics Worldwide: State of the Art in Soilless Crop Production conference brought considerable attention to the NFT technique (Savage, 1985). The NFT system is relatively inexpensive to install and maintain, and is quite precise in its control of the nutrient element-root environment as described in Cooper’s most recent book (Cooper, 1996).

The first major NFT application was for the growing of tomato plants in a controlled environment.  A rockwool cube in which a young tomato plant had been germinated is set in a sloping trough (or channel) of flowing nutrient solution. One type of trough consists of a plastic sheet that is pulled up over the plant containing-cube, enclosing it in a pyramid-shaped tent.

However, the NFT technique was found to have a major flaw. As the root mass in the NFT trough increased in size and filled the trough, the flow of nutrient solution down the trough was impeded, the nutrient solution flowing around and over the top of the root mass rather than passing through it. An anaerobic condition then develops, followed by partial death of roots within the root mass. Altering the design of the trough to a “W” configuration (the plant sits on top of the center peak and roots grow down wicking material into the two troughs on either side of the peak) significantly altered the potential for root clogging of the trough and the incidence of root death. However, the technique still presented problems in maintaining suitable environments for the best root function and plant growth.

The slope and length of the trough as well as the rate of nutrient solution flow down the trough can significantly effect plant growth depending on plant position, whether at the head or foot of the trough. Smith (2004) has written an excellent short history of NFT gully (trough or channel) construction and use.

Discarding the nutrient solution after leaving the NFT trough is wasteful of both water and nutrient elements; therefore the nutrient solution is collected and re-circulated. One additional recirculation can be done with little effect on plants, but further reuse requires that the nutrient solution be filtered to remove suspended organic matter, sterilized to kill disease organisms, and nutrient elements added to bring the elemental concentrations in solution back to their original set levels. Some NFT systems are designed so that air, or even pure oxygen (O2), is bubbled into the nutrient solution to increase its oxygen content before being discharged into the NFT trough in order to prevent oxygen starvation which leads to root death.

Today it is generally accepted that the NFT technique is not suitable for use with long-term crop plants, such as tomato, but has been found a suitable method for short-term ones, such as lettuce (Meade, 2002) which is ready to harvest before the plant roots fill the trough.

J. Benton Jones, Jr. has a PhD in Agronomy and is the author of several books including Hydropopnics: A Practical Guide for the Soilless Grower. It is available at http://www.crcpress.com/. Dr. Jones may be contacted at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

References:

Cooper, A. 1976.  Nutrient Film Technique for Growing Crops.  Grower Books, London, England.

Cooper, A. 1996.  The ABC of NFT Nutrient Film Technique.  Casper Publications, Narrabeen, Australia.

Meade, A. 2002.  Soilless lettuce in the South Pacific.  The Growing Edge 13(4):40-43.

Savage, A.J. (Ed.). 1985. Hydroponics Worldwide: State of the Art in Soilless Crop Production.  International Center for Special Studies, Honolulu, HI.