The recirculating pump?
This pump must have the capacity to pump enough fluid to keep the system operating. It must be designed to handle the corrosiveness of the nutrient solution. A non-corrode pump will usually be adequate. In small NFT systems, a fountain pump is often used with success. Although a fountain pump is not designed to take much in the way of back pressure, it can be used in a small NFT system which has minimal back pressure in the delivery system. The amount of lift required by the system should be three feet or less, which means the level of the nutrient solution in the reservoir should be no more than three feet. It is always better to have a pump that is a little larger than what is needed, rather than one which is marginal or too small in capacity. The capacity of the pump (as stated on its packaging) should be about five times the amount in gallons per hour than is needed.
Locating there will also circulate the nutrient solution in the reservoir tank, keeping the nutrients mixed. In this type of NFT system with plants in the lettuce-size range, the nutrient solution can be circulated through the channels 24/7. This means that there is no need for a timer to turn the pump on and off. This simplifies the setup and operation of the system. It also eliminates one of the potential costs in the system.
Irrigation Lines and Emitters?
Flexible poly pipe, of the kind used for irrigation applications, is used to deliver the nutrient solution from the pump to the emitters that deliver a controlled volume of solution to each NFT channel. The advantage of the flexible poly pipe is that it allows you to directly insert an emitter into the poly pipe without separate connections. It also allows an emitter to be placed where it is needed along the length of the pipe. Rigid PVC pipe is often used in larger NFT production systems between the pump and the flexible poly pipe of the nutrient delivery system. Larger PVC lines are used to deliver the larger volumes of solution to different zones of an NFT system.
Although this can be done in small systems, it is not necessary and is usually avoided because of the cost of the connectors compared to a few extra feet of poly pipe. Emitters for a small NFT production system using small fountain type pumps should be non-pressure-compensated emitters. Small fountain type pumps do not produce the pressure needed for uniform delivery when using pressure compensated type emitters. Only larger systems with higher flow rate requirements that use centrifugal type pumps can utilize pressure-compensated type emitters. However, even larger systems seldom use pressure-compensated emitters. With a properly designed system with a balanced flow rate that runs continuously, there is no need to use pressure-compensated emitters for even delivery. It would only be an unnecessary extra expense, and in some instances may possibly cause nutrient delivery inconsistency to some or all of the NFT channels.
The drain line catches the nutrient solution after it has left the NFT channel and returns it to the reservoir to be re-circulated. The drain line can be made out of three or four inch PVC pipe and the necessary fittings. Polyethylene sewer and drain line is used by some growers because it is white on the outside and black on the inside. The black color blocks out light that can support algae growth on the inside of the return line. The white exterior reflects some of the light and heat to minimize temperature increase in the fertilizer solution in the return line. The way the drain line is cut for receiving the solution from the NFT channels depends upon the design of the channels and the overall system. Some NFT channels have drain end caps and channel the solution out through PVC fittings that will slip through holes drilled in the drain line.
Other channels just end without a cap and drop the nutrient solution into a cut in the return line or an open gutter. The downside of this method is that some of the solutions may not drop into the hole or cut in the return line, and will be spilled and lost. Soluble fertilizers must be used in the NFT system. The fertilizer solution is the only source of the needs of the plants other than the air. In this system, if it will not dissolve in water, it will not be available to the plant through the roots.
The Electrical Conductivity (EC) is used to monitor the strength of the fertilizer solution being delivered to the plants. A conductivity meter should be considered an essential part of every NFT system. A reliable instrument-quality conductivity meter should be chosen. It will cost a little more, but is far superior to any of the “toy” conductivity meters on the market. PH is a measure of the acidity or alkalinity of a water solution. This information is important in a fertilizer solution because it affects the solubility and the availability to the plant of the different fertilizer components. Therefore, its important to keep the pH of the recirculating nutrient solution in the correct range.
Measure the pH with a colour indicator kit or a pH meter. The re-circulating solution should be checked at least once a day. A pH meter needs to be calibrated regularly in order for it to be reliable. The probe unit of a pH meter is usually only guaranteed for a year or two, and it may only last that long or a little longer. The probe should be replaced if the meter is giving unrealistic or inconsistent readings. Be prepared to replace the probe at the end of its guaranteed life.
The writers are affiliated with the Ohio Agricultural Research and Development Center, Ohio State, USA.