P
lants have developed a good working relationship with
many of the microbes naturally present in their growing
environment, and this is not limited to just soil-based crops.
Anywhere there is moisture, nutrients, and a supply of organic
carbon, microbes will thrive, and hydroponic systems are no
exception. In the early days of soilless systems, it was thought
that a clean and sterile approach to hydroponic cropping
was ideal, with the elimination, or at least reduction, in fungi
and bacteria in general being the objective. However, a more
modern approach has embraced microbial diversity and
now hydroponic growers have a wide selection of inoculant
products for use in their production systems. While this has
been a significant step forward in understanding and utilizing
nature’s forces to overcome pathogens and enhance growth,
there is still a lot to learn about microbial interactions and
how we may harness these to our best advantage.
e
h
t
’
n
Rocki
by Dr. Lynette Morgan
Understanding the benefits of
microbial life in the rhizosphere
of your hydroponic plants will go
a long way to growing healthy,
productive crops. But how do you
monitor and adjust something you
can’t see? Lynette Morgan explains.
PLANT GROWTH-PROMOTING RHIZOBACTERIA
Plant growth-promoting rhizobacteria (PGPR) are bacteria
capable of promoting plant growth by colonizing the plant
root system. They can be divided into two groups: symbiotic
bacteria that form an association with the plant, and free
living rhizobacteria that are present in the root zone but not
reliant on a direct association with the root system or plant.
Beneficial microbes may be most well known for their
protection against a number of root pathogens, however, they
have a much greater potential under hydroponic production.
Relationships with beneficial microbe populations in the
rhizosphere occur in hydroponics just as they do out in the
field, with diverse and beneficial microbe species present in a
wide range of different soilless systems. Root exudates, which
are the release of organic compounds from the root system,
were once seen as a potential problem in hydroponics due
to the belief that they would build up in the root system and
restrict plant growth. However, root exudates, which represent
between five and 21 per cent of the photosynthetically fixed
carbon, are used by the plant to attract and select certain
microorganisms in the rhizosphere. These microbes can then
work, via different mechanisms, to influence plant health
and growth. For example, root exudates act as signals that
encourage and initiate a relationship or symbiosis with
rhizobia and mycorrhizal fungi, as well as rhizo-bacteria,
which is beneficial for both microbes and plants.
Relationships between beneficial microbes in the
rhizosphere occur in hydroponics just as they do in soil.
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Maximum Yield