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Growing Knowledge
to Grow Success
Take the luck out of growing successfully!
Featuring Harley Smith, director of research for Grow University.
Microbial Inoculants
By Harley Smith
Organic growers have known for
years that healthy soil grows healthy
plants. But what makes some
organic soils better than others?
The answer lies in the rhizosphere,
the area closest to the root zone
where root cells and microbes
interact. Plants can’t take up
large organic molecules. Organic
fertilizers must first be broken
down by microorganisms before
they can be efficiently taken up
by the plant. In the process, some
beneficial microbes also produce
biologically-active molecules that
stimulate plant growth and improve
the plant’s natural resistance to
pests and disease. That’s where
microbial inoculants come into
play. By selecting specific strains of
microorganisms from the most fertile
soils and applying them to the plant
as a root drench, it is possible to
enhance the performance of any soil.
All microbial inoculants are not
alike. Some microorganisms in
the rhizosphere complement one
another, working together as a very
efficient team, while other microorganisms compete with one another.
The key is to assemble a team of
microbial superstars that work well
together and have the greatest impact
on the plant. For example, some beneficial bacteria are great at snatching
nitrogen out of the air and changing it into fertilizer. Other bacteria
are better at unlocking phosphorus
from the soil. And other microbes
are experts at making natural growth
hormones and plant protection
agents. Put them together in just the
right way, and you have a dream team
that provides a synergistic effect on
the plant. In fact, the right combination of microorganisms will feed each
other while feeding the plant!
Many potting soils advertise the
fact that they contain mycorrhizae,
but mycorrhizal fungi alone provide
only limited benefits to the plant.
For example, if there is a phosphorus deficiency in non-fertile soil,
plants will exude signal molecules to
attract mycorrhizal fungi. The fungi
penetrate the root cells, feed on
sugars manufactured by the plant,
“the right combination of
microorganisms will feed each
other while feeding the plant!”