From a grower in Texas
Your article titled ‘What are the fundamentals of setting up an NFT system?’ in PH&G issue #148 was very helpful. I am setting up a scaled-down NFT system in my greenhouse to run a basil trial. I have set it up with 4” rectangular grooved downspout channels that are 40’ long and I am supplying 0.5 litres of solution to each channel, as you suggested in your article. I have the channels sloped on a 40 to 1 ratio, which brings me to my question. In examples I have found elsewhere on the Internet most folks upon transplanting raise their drain tubes in order to raise the solution level to the bottom of the net cups in order to ensure the infant plants come in contact with the solution. They later lower the tubes back down when the plants have matured and the roots can lie on the bottom of the channel. This is not possible with the 40 to 1 slope; you just end up flooding one end of the channel. I was wondering what you normally recommend doing in these sloped systems? Also, the 0.5 litre flow rate seems like just a trickle to me and as it meanders down the channel it may only be in one or two grooves on one side or the other. In other words the solution is not evenly spread over the bottom of the channel. Thanks in advance for your help.
Answer by RICK DONNAN
Thanks for your interesting and detailed question.
Hobby NFT systems
Your question clearly shows the difference between commercial and hobby NFT systems. Because hobby systems invariably use relatively short channels there is very little limitation in how the system is set up and managed. For example, aspects such as channel shape, slope, and flow rate are largely up to the hobby grower to choose, virtually without associated problems. That is, there are a wide range of set-ups and techniques that will give OK results.
My only suggestions to users of these systems are:
- Buy an EC meter and keep your EC under modest control.
- Have a bypass line after your pump spraying back into your tank to maximise aeration.
- Responsibly bleed or discard some used solution regularly to avoid nutrient imbalance.
For commercial farms there are many aspects which are more important than for the hobby grower, such as yield, consistent quality, capital, operating and labour costs, etc. Long-term success will depend upon being able to satisfy the market and receive a reasonable price.
Slope of long channels
From what you have written I assume that the net pots you use have a flange on top, which then holds the pot above the bottom surface of the channel. This gap creates problems if you start the plant direct into the channel and, as you quote, hobbyists can overcome this by raising the drain tube to flood the channel. This is not an option for commercial growers. Holding up a 20 or 40 ft (6 or 12 m) channel to flatten the slope is unworkable and indicates one reason for the 1 in 40 slope, which is that the channels will deflect into a dip between supports. The rigidity of the channel when loaded with mature plants and water will determine the minimum spacing needed between supports.
All commercial NFT systems in Australia (total area about 100 hectares (250 acres) start their plants outside of their production channels. A wide range of blocks and set-ups are used to do this. Typical options are rigid blocks such as rockwool and foams, Jiffy pots, assorted media (usually based on cocopeat) started in cell trays, and media in net pots. Importantly, the net pots used do not have a flange. Consequently the critical difference to what you are doing is that all starting blocks rest directly on the base of the channel when transplanted. That is why it is important for the channels to have some means of centring the flow so solution will touch each block. Touching just one part of the block is enough for capillary action to wet the whole block. Without central ribs, grooves, or curve the flow will ‘snake’ down the channel regardless of the flow rate. With these blocks and channels there is no need to flood the channel when transplanting. With time the roots grow across the channel to give more of a film.
Some techniques for starting plants are:
- Cell trays holding media watered on ’flood and drain’ tables, or hand watered.
- Small channels closely spaced to hold close packed blocks. Some growers use small diameter round pipes, others narrow open channels.
- Channels which have independent lids. Growers remove the lid and close pack the blocks in the open channel.
Most of these systems are fed flood and drain (also known as ebb and flow.
In any NFT system the flow rate can be increased to whatever rate you want. The limitations are to not flood the channel, and it is also possible for a high flow rate to wash plants down the channel. In a commercial farm with perhaps thousands of channels, then the pumping cost can be significant. So the figure of 0.5 litres per minute is adequate for small plants. To go higher is OK, but it costs more to buy and operate the pumps. If there is excess pump capacity I would prefer to see it used for bypass aeration as described above. RD