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Article 3-3 NFT Gully

by Mick Lanyon

The use of hydroponic channel has now become the method of choice for growing in commercial hydroponic systems. This is especially true for tomato, strawberry, lettuce and herb growers. This system is pure hydroponics where the plant sits in the channel with the roots of the plant only coming into contact with the nutrient flowing through the NFT (nutrient film technique) system. An NFT system means that media's such as scoria, sawdust, gravel, river sand, and peat used in other systems such as 'drip to waste', is not required. While this method appears to be very simple in practice, in reality the end result for the grower will depend on the type of channel used and how the system is set up and run.

When utilizing NFT systems, it has been demonstrated that there is a definite advantage in terms of yield over other methods currently being used. Also, there are substantial long-term savings using channel. Rapid turn-around at the end of each crop reduces significant labour costs, while not having to purchase new growing mediums and growing bags etc, means further savings.

The main feature of NFT, is a 'film' of nutrient passing by the roots of the plant and therefore the design of the gully is a major consideration when planning for a commercial system. The channel should be designed in such a way as to ensure the nutrient runs down the centre of the channel. The depth of the channel should have sufficient space between the roots of the plant and the top of the channel. This space is to allow for oxygen, entering through the holes provided for the plants, and to facilitate the removal of waste gases. The roots in contact with this film can take up nutrient while others not covered by nutrient are able to take up oxygen. These gases that are heavier than air, flow out with the nutrient returning to the feeder tank. The use of flat bottom channel should be avoided, as it is nigh impossible to ensure the nutrient will flow down the centre of the channel. The use of round pipes negates the 'film' technique, which is the basis of this method of growing. In round pipe, the nutrient flow is a lot deeper, as the roots cause damming between each plant. That is, as the plant matures and the root mass grows bigger, the nutrient level rises in the pipe and the space necessary to carry out the waste gases and provide appropriate oxygen uptake is markedly reduced. In addition to this, set up costs can also be greater as the round base does not readily apply itself to the standard flat stands.

It is also important that the channel has good longitudinal strength. If allowed to sag, damming will occur as seen in the round pipe. Poor strength will also add to the costs, as additional stands would be required to eliminate this problem. One of the most important features when choosing an NFT channel, is whether or not it comes in one or two pieces. That is, does it come with a base and lid, or just a single one-piece pipe? Most growers would agree, that easy access to cleaning your channel be essential. The two piece channel allows the grower to not only clean his channel quickly and most important effectively, but also rapid turn-around means less labour costs. Another important aspect, is access to the channel to remove dead or dying plants that can not only cause blockages, but to remove this organic waste before it breaks down and enters the nutrient. The removable lid also gives the grower the option of using other growing systems. For example, when the lid is removed the channel may hold a growing medium to use in a drip feed system (eg. Growool/Grodan/Pargro etc.), or scoria for a flood and drain system. In each case, the nutrient can be collected and not wasted. This fact should be a major consideration for prospective growers, as it is anticipated that future government legislation will prevent growers from draining to waste.

Update
Since the Fall/Winter 99 article on NFT Systems, I have been doing a little travelling and attending some Trade Shows and also visiting with growers in Australia, New Zealand and the US. During this time I have picked up some interesting information on NFT Systems, some of which conflicts with my earlier article. So like all good editors, I felt it only right to update the readers.

As I stated in my previous article, a problem in the past with old style NFT Systems was that the polyethylene film tended to collapse against the plant stems, causing amongst other things, serious gas exchange problems. It is essential where possible to maximize the 'space' between the nutrient and the top of the channel to facilitate this gas exchange.

Therefore, the design of the channel is a major consideration when planning for a commercial system. The channel should be designed in such a way as to provide for gas exchange, and to ensure that the nutrient runs down the centre of the channel. Have you ever dropped water onto a flat surface? If you have, you'll know that it is impossible to control or even determine which way the water will run. To correct this problem, the channel should be relatively flat with a concave base (approx. 1-2mm). It is also highly desirable that the depth of the channel allows for sufficient space between the roots of the plant and the top of the channel. This space is to allow for oxygen, entering through the holes provided for the plants, and to facilitate the removal of waste gases. These gases that are heavier than air, flow out with the nutrient returning to the feeder tank (make sure your holding or feeder tank is appropriately vented). The use of round pipes may be cheaper in cost, but can pose a major problem as the plants mature. Keep in mind, that the main feature of NFT, is a 'thin film' of nutrient passing by the roots of the plant. The roots in contact with this film can take up nutrient while others not covered by nutrient are able to take up oxygen. In round or oval pipe however, the nutrient flow is a lot deeper as the roots cause damming. That is, as the plant matures and the root mass grows bigger, the nutrient level rises in the pipe and the space necessary to carry out the waste gases and provide appropriate oxygen uptake is markedly reduced. In addition to this, set up costs can also be greater as the round base does not readily apply itself to the standard flat stands.

In my earlier article, I also noted that in old NFT systems, roots were squeezed into a very dense root matt. To clarify, this was not because it was an NFT system per say, but simply because of the restricted area roots were given to grow in. Allowing room for plant roots is the simple remedy for gas exchange, root rot or other root diseases. Some manufacturers produce channel in various sizes. As someone recently said to me "Would you try to grow a 20' Maple tree in a 2" Pot?" No, not likely. But given the growth hydroponic technology in recent times I am not prepared to say it can't be done! So the same principal applies to hydroponics to some extent, in that the size of the plant will determine the size of the channel.

The rigid PVC used in NFT channel production today should be strong yet flexible and must be UV stablized. It is also important that the channel has good longitudinal strength. If allowed to sag, damming will occur as seen in the round pipe. Poor strength will also add to the costs, as additional stands would be required to eliminate this problem. The channel is generally supported every 3-4' depending on the plant, and the angle on which they are laid (approx. 40 : 1) ensures nutrient flows down the channel preventing stagnation or pooling. Two piece channel, ie, lid and base, is highly desirable to facilitate good access for cleaning and the removal of dead or dying plants that can cause blockages. More importantly, it is essential to be able to remove this organic waste before it breaks down and enters the nutrient. The removable lid also gives the grower the option of using other growing systems. For example, when the lid is removed, the channel may hold a growing medium to use in a drip feed (eg Growool) system or scoria for a flood and drain system. In each case the nutrient can be collected and not wasted. This fact should be a major consideration for prospective growers, as it is anticipated that future government legislation will prevent growers from draining to waste. One piece channel may cost less, but denies the grower essential access for 'servicing' and cleaning.

While net pots set into the top or cover of NFT Channel is a pratice still widely used in NFT hydroponics, this too is changing. The main reason for this is the cost factors versus the necessity. More and more commercial & hobby growers now are 'dropping' their seedlings (grown in rockwool cubes) directly into the channel through appropriate sized holes in the cover of the channel and in direct contact with the nutrient. This results in a fast and high yielding crop where double handling and capilary mats are eliminated.

Another point made was the use of air pumps and misters. In reality, in large commercial systems this method while good in theory, may not be in practice. The problem most often encountered is blockage of the 'misters' with seed or other organic matter. Feeder tubes (4mm diameter), two to each channel, will provide sufficient nutrient to meet the 1-1.5litre per minute requirement. The low cost, easy to install 'venturi systems', provide ample aeration to the nutrient.

The applications of NFT channelling today is vast. The versatility of two piece NFT channel can be demonstrated by the wide variety of uses in commercial systems today. Essentially, the two piece channel is used for standard NFT systems growing traditional crops such as lettuce, herbs and tomato's. However, by using a variety of combinations, of base and lids, systems such as 'drip', 'flood and drain', 'deep flow' and 'spray', are now being used. As the channel is available in sizes from 4" wide x 1 3/4" deep to 9" wide x 3 1/4" deep, you can grow almost any crop you like using NFT channel.

With all of the advancemens in NFT Systems today, both the growers and manufacturers alike agree on one thing - Keep it simple. So. . . there you have have it... the latest, up-to-the-minute news on NFT Systems.

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