This is page 3 of our twelve page series on nutrient film technique. Click any of the below pages to jump to that page.
Here is a variation on the theme of mixed crops, at mixed ages, in one system. Note that different crops and different ages occur within a single channel. The irrigation cycle for that channel would therefore need to meet the needs of all the crops at their various life stages.
Nutrient film technique does have a few drawbacks, which are typically avoidable if you’re careful with design, management and maintenance. First, the slope of the channel is critical to the proper flow of nutrient solution through the channel and over the roots. If the channel is too steep, the nutrient solution will run over the roots too quickly and the plants won’t have a good chance to absorb the nutrients. Alternately, if the channel is too close to level, the nutrient solution will linger too long and the roots can become waterlogged or simply drown. When buying a turnkey NFT system, check with the installation instructions for the proper angle, and make sure you provide that angle when assembling the system. If you’re building your own, check functional systems which are growing the crop(s) you are interested in, and match the slope of those channels as closely as you can. Varying the angle by even a few inches over a 10’ length can make a huge difference.
Secondly, the type of crop you wish to grow will determine the slope of the channel, the depth of the channel, the spacing of the plants, and the frequency for cycling the nutrient solution. Again if buying a turnkey NFT operation, these variables should already be worked out for you. However, if you started with one crop and eventually switch over to another crop, you will need to to revisit all those variables and probably make some changes.
A third disadvantage is that the nutrient solution will vary slightly from the point it’s put into the channel to the point it leaves the channel, during a single irrigation cycle. This is because the plants at the front of the channel, ie the plants that get nutrient solution first, will take some of those nutrients out of the solution. When the channel is long enough for dozens or even hundreds of plants, that can result in measurable differences between the nutrients at the near end versus the far end of the channel. That might seem just an annoying little detail, but the plants at the far end of the channel can thus be deprived of sufficient nutrients if the nutrient solution gets a little weak. So nutrient solution concentrations need to be checked frequently. If anything, the nutrient solution should be kept a little rich to help ensure that all the plants in the channel have sufficient access to nutrients.
The above issue also limits how long the channel can be. There is a functional limit to the length of those channels since the nutrient solution will gradually get weaker and weaker with each additional unit of length. If buying a turnkey system, that system will have specific guidelines for how rich the nutrient solution needs to be for the given length of growing channel(s). Don’t vary that length unless/until you check with the system builder to see how different lengths will change the nutrient solution concentration.
A fourth issue with nutrient film technique is that some crops can develop such thick root mats that the nutrient solution has a hard time penetrating that mat, and providing good nutrition to the plant. This issue is usually reserved for large plants which have been in the system for a long time, such as older tomatoes or other vine crops. Those crops are not as commonly found in nutrient film technique systems as shallow-rooted plants such as lettuce, so it may not even be an issue depending on the crop(s) you’re growing. Just be aware that the older the crop, the bigger the root mat will be, and the more carefully you need to monitor whether the crop is getting enough nutrients.
Finally, this system is also prone to both flooding or drying out, if either a blockage or crack occurs somewhere in the system. If the blockage occurs at the point where the nutrient solution enters the channel, the entire channel can dry out very quickly, even within a few hours in some climates. If the blockage occurs somewhere along the channel, then the plants upstream of the blockage can drown, while the plants downstream can dry out. If the blockage occurs at the end of the channel, the entire channel might drown. If there’s a leak or crack somewhere in the system, insufficient nutrient solution will be circulating to the plants, starving them of nutrients and possibly allowing them to dry out. Alternately, such a leak can also flood the surrounding work areas.
One of the common questions we get about hydroponics is whether it can be automated to the point where human intervention and maintenance isn’t needed. Whenever we get that question, we can very easily answer with a resounding “No, you still need to check the system several times a day”. The above scenarios are a big part of why. The whole point of hydroponics is to make the systems as efficient as possible, and well-designed systems make that possible. However, they still need to be monitored. Small problems can turn into big problems in a big hurry. Nutrient film technique is not unique in this regard; all hydroponic systems need to be monitored. But NFT is unique in the sense that if something goes wrong, there isn’t much of a safety net to hold plants over until the situation can be resolved.
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