Analyzing nft
The Trays or Gutters
The ideal NFT system uses trays or gutters with completely
flat bottoms to allow for the film of nutrients to develop. The
flatter the surface, the larger the surface area that can be
covered in a nutrient film which, in turn, gives a larger surface area for the plant’s roots to feed. The larger the surface
area of nutrient film, the larger the exposure to air around
the root mass. A high air-to-nutrient ratio creates the perfect
environment for stimulating root growth. Tubes (like PVC
piping) or trays with ribbed or shaped bottoms are generally
not the best choices for NFT systems. The water will pool,
which minimizes the surface area of the nutrient solution,
thus lowering the air-to-nutrient film ratio.
The Pump
The key to a properly operating NFT system is the flow of
nutrient solution. To figure out what size pump is needed,
the grower must first determine the necessary head height. A
pump’s head height is the maximum height to which liquid
can be delivered. For example, if a pump’s head height is 4 ft.
then it has the capability of delivering liquid 4 ft. vertically.
Above 4 ft. and that particular pump would no longer be able
to deliver liquid because the weight of the liquid itself becomes
greater than the forces attempting to push it.
To determine the needed head height of the pump for an
NFT system, a grower should measure vertically from where
the pump will sit in the reservoir to the point of delivery.
Add about 20% to your needed head height measurement
to ensure your pump will be able to do the job. It is always
better to have a pump that is slightly overpowered rather
than one that is underpowered. Once you have determined
The key
to a properly
operating NFT
system is the
flow of nutrient
solution.”
102
Maximum Yield USA | February 2014
the necessary head height, you can purchase a pump for your
system. Because NFT systems do not require a large volume
of water flow, it is best to choose the pump with a maximum
head height closest to your measurement without being
under. Head height and GPH (gallons per hour) should not
be confused, although as one increases, in most cases, so
does the other. Growers using NFT systems should choose
the pump with the lowest GPH that still meets the minimum
requirement for head height.
Once the pump has been chosen, the grower can start to
modify the flow to create the perfect film in the gutters or trays.
There are a few ways a grower can control this but the easiest
and most precise is to use a pump that has an adjustable flow
rate. Pumps with adjustable flow rates are perfect for NFT
systems. They allow the grower to adjust the flow directly from
the source—the pump. Another effective way to control the
flow in an NFT system is an inline valve connected at the point
of delivery. An inline valve at the point of delivery and a pump
with an adjustable flow rate are the ultimate combination for
controlling the nutrient film. Once the system is in place and
the pump is adjusted, a continuous film of nutrient solution
should cascade down the trays or gutters. It is important to
remember that as the plants grow in the system, it may be necessary to make slight adjustments to the flow rate. It is always
good to monitor the last tray or gutter in the system to ensure
it is still receiving adequate
nutrient solution
once the plants
have become
established.