The Real Problem With Bogus NFT

 

It’s never a bad time to reiterate what Nutrient Film Technique (NFT) is and is not and why it's important to know the difference. I want to make it clear right away that this is not about what will or will not grow plants. Many systems with superficial resemblance to NFT grow quite well while meeting none of the design specifications of NFT and while using an entirely different theory of operation. I feel fairly confident in saying that here and among home hydroponic growers in general, the vast majority of purported NFT systems are simply not NFT. But don’t go showing me your “NFT” system you made out of pipes and how well it grows. I’ll bet it grows just great. But reserve your claim to it being NFT until later.

NFT was brought into the light in 1965 by Allen Cooper at Glasshouse Crops Research Institute in England. His book, ABC of NFT is a classic and nearly impossible to find. NFT has specific benefits for commercial growers. It also presents some exposures not present in other hydroponic methods.

To begin, I will ask that we adjust our thinking by eliminating some mental images and including others. First, cast out all images of round pipes. The curved walls of pipes are almost precisely the wrong shape for NFT, although perfectly good and far more tolerant systems can be made using pipe. I also want to cast out the common alternative materials, vinyl downspout and vinyl fence post. It’s not that they wont work well for NFT, but their proportions mask one of the specific features of NFT.

Unfortunately, we also have to cast out most of the images of “NFT” systems to be seen on the Internet.

Some are diagrams are absurd attempts to represent an NFT system. A typical example:

And the many misrepresented Chinese pipe systems offered on Amazon and eBay and the Chinese direct sales sites.

 

We will concentrate instead on actual purpose-made NFT channel.

 

This is a good image for discussing NFT specifications because of the obvious attribute of the channel – it is short and wide. You could not possibly have enough free air space to have roots in. As we will see as we go through how NFT really works, there’s a reason it can be short. And being short is a positive attribute for commercial operations which are so often vertical farms like this one.

 

Vertical space has real value in these operations and should not be squandered if the goal is to maximize production.

There is a common mistaken belief that in NFT the roots obtain air from being in open free air above the nutrient flow. But even a cursory look at the cross-section of NFT channel should put that notion to rest. There’s no room.

Here’s what it looks like inside a CropKing NFT channel. Note how the roots are able to fan out across the width of the channel in the wide, very shallow flow. Channel can be up to ten inches wide.

 

Another view inside a channel.

 

Dutch bucket systems provide some perspective here. In a Dutch bucket, a small flow of nutrient solution is injected into the region near the root crown. The solution drizzles in a meandering way down the roots or though the medium and roots, clinging to them in a thin film and finally running off to be drained away. Dutch buckets require no mechanical aeration of the nutrient. Roots have easy access to air with the very thin films of nutrient clinging to them and wandering down randomly through them.

That leads to the first hallmark of NFT and one often missed by the casual observer who has mostly seen channels of larger cross-section that lead to the erroneous conclusion that the roots in air above the nutrient are the main source of air.

In NFT, the roots exposed to the nutrient solution are the roots with air access, just as in Dutch bucket. This means proper NFT must provide the merest thin film of nutrient, as Dutch buckets provide. Roots must be able to fan out across the relatively wide flat bottom of the channel so that a low flow of nutrient can find its way through the root fibers without submerging them, again, just as roots in a Dutch bucket are fanned out in the air or through chunky, inert medium. If submerged, they would drown because the nutrient is not aerated. Were the nutrient aerated and flowing at such a slow rate and in such a thin film, dissolved air would be lost long before the last plants in the channel had an opportunity to take it up. It can happen in a Dutch bucket when the roots clog a drain, and it can happen in an NFT channel for the same reason.

So, because there’s no worry about dissolve air being consumed, one of NFT’s great advantages is that all the plants are equally served.

This cannot happen in pipe used to attempt NFT. Pipe offers a limited width of curved floor. Roots are submerged and have little room to fan out. In fact, in all circulating pipe-based systems that don’t have very large pipe with a high-radius arc, the curved shape tends to cause roots to trail into the deeper center and form narrow tangles and are not well fed or aerated. And they cannot reach atmospheric air through the deep flow of hypoxic nutrient, so nutrient must be aerated, and that takes it out of NFT design.

Pipe, preferably larger diameter pipe, can be used by trailing a root mass in a relatively deeper flow of nutrient and leaving a relatively large root mass above the nutrient in free air. But after the depth of the net cup or other support is accounted for, it requires a large pipe indeed to do it right. And it is, of course, nothing to do with NFT.

The most difficult problem in NFT is maintaining the mere thin film so that it clings to the roots as it passes through but does not block access to air. The flow is typically low, one liter per minute. And the slope of the channel is carefully controlled. Slopes from 1% to 4% have been explored. Each has potential problems and potential benefits. And the channel must be supported so the bottom is entirely flat with no bumps of low spots. Channels must be drained by zero clearance bulkhead connectors or as is often done, simply leaving the drain end open.

One of the trade-offs of roots being allowed access to air as the nutrient film flows through them is that the slope and length of the channel together have significant effects on plant growth according to where along the path the plant is installed. The benefits of NFT are best realized in a large commercial operation where the painstaking development of these issues can be done once for the one crop being grown and replicated over tens of thousands of square feet and through dozens of vertical layers.

NFT presents the very real hazard of roots filling the channel. There have been attempts to avoid the problem with new channel designs, but they have mostly just introduced new problems. It is one more reason NFT is suited to commercial growing of short-life plants where the system is constantly monitored.

Some NFT operators have indeed injected air in the nutrient flow at the point where it enters the channel, but that defeats one of the most attractive aspects of NFT. And NFT is unsuitable for long-lived and large crops like tomatoes.

In the end, design of any hydroponic system, if one is to get full benefit rather than just something good enough that plants will grow in, is to carefully attend to the basic needs of the plants. We have seen how in NFT, the essential requirement for air demands meticulous design, because NFT channel and small diameter pipe used with deeper flows allow for very limited free air space for roots without more or less elaborate arrangements for plants to be supported above the pipe, and it’s still not really adequate as an access to air. And in pipe, the shape of the pipe inevitably forms the roots into a less then desirable mass, unless the pipe is relatively large and the nutrient runs relatively deep.

One need not give up pipe or pipe-like tubes. Both can be used in Deep Water Flow systems if the pipe or channel is sufficiently large to provide both adequate nutrient and plenty of air or if nutrient solution is well-aerated. But to use such system to best advantage, one must stop thinking of them as NFT and recognize that designs need to be optimized as much as possible in ways that do not apply to NFT. The first step in constructing a pipe system is to define what it’s actual theory of operation must be and to work within it.

In my opinion, the two materials best suited for tube type systems are vinyl fence posts and vinyl downspouts. Both have end caps available. Both are rectangular with flat bottoms that avoid training roots into training stringy masses and wide enough for them to fan out. And both are deep enough to allow a respectable flow of aerated nutrient at a flow rate that is not critical. And the rectangular cross-section maximizes the amount of nutrient that can be flowed. They become essentially elongated recirculating deep water culture systems, a simple and forgiving method.