See
Fig 5.1. NFT provides no medium support for roots. Typically,
roots sit in a long sloping irrigation channel. Nutrient is
introduced at the high end and allowed to flow over the roots after which
it drains into a nutrient reservoir. It is then re-pumped back into
the channel to repeat the watering process.
This
feed cycle can be intermittent (“pulsed” NFT i.e. repeated many times per
hour) or continuous (as practiced in many commercial operations). Note,
pulsed NFT usually achieves better aeration of roots because roots are
exposed to air between feeds.
Some basic design requirements are:
+
For drainage, channels need suitable slope (i.e. gradient 1:40).
+
Channels must be wide enough to cope with potential root volume otherwise
they can become “choked” with roots. This can cause damming, overflowing/
flooding or create stagnant areas that fail to drain fully.
+
To avoid blockage of the drain, the last plant should be positioned well
upstream of the drain’s outlet.
Advantages to NFT
+
Lower water and nutrient consumption / costs.
+
Avoids the supply, disposal and cost problems associated with medium based
systems.
+
Relatively easy to sterilize roots and hardware compared to other system
types.
+
The absence of medium makes it easy to inspect roots for signs of disease,
feed adequacy, etc.
+
Regular feeding prevents salt build-up in the root zone and maintains
satisfactory root zone pH and conductivity.
+
Environmentally friendly - minimal potential for localised groundwater
contamination.
Disadvantages to NFT
+
Pump failure can result in plant death within a few hours, especially in
hot weather.
+
Not suitable for plants with large tap-root systems (e.g. carrots).
+
Compared to run-to-waste systems, it is less suitable for saline (salty)
waters because the salinity of the recirculating water gradually
increases.
