provides no medium support for roots. Typically, roots sit in a long
sloping irrigation channel (Fig 1.1).
Nutrient is introduced at the high
end of the channel 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 or
continuous. An ‘intermittent’ feed cycle is regulated by a timer and
repeated many times per hour. It is sometimes termed “pulsed NFT”. Pulsed
NFT usually achieves better aeration of roots because roots are exposed to
air between each feed. A ‘continuous’ feed cycle runs non-stop. This is
often used in commercial operations.
design requirements for NFT are:
- Channels need
suitable slope for drainage (i.e. gradient 1:40).
Channels must be wide and deep enough to
comfortably accommodate the plant’s mature root system.
Undersized channel’s can become choked with roots which can lead to
damming, overflowing or create stagnant areas that fail to drain fully.
The last plant should be positioned well upstream of the drain’s outlet so
that roots do not block the drain.
- Growth problems can occur as
the channel length increases. For example, commercial NFT systems often
use channels that are several meters long e.g. 5-10 meters. Plants at the
head of these long channels often perform better than those at the
‘outlet’ end. Keep this in mind at the design stage. The threshold length
will depend on factors such as the type of plant being grown and the
nutrient strength. Note that increasing the nutrient flow rate will help
alleviate these problems.
Advantages to NFT
- Lower water and nutrient consumption.
- Avoids the supply, disposal and cost
problems associated with media based systems.
- Relatively easy to
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 (and associated
flushing) prevents localised salt build-up in the root zone and maintains
uniform 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.