Hydrolife Canada February/March 2017

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IDEAL CO 2 LEVELS
One of the most hotly debated
aspects of CO 2 fertilization in
cannabis cultivation is the proper
concentration of CO 2. The only
cannabis-specific research done
is this area is presented in Dr.
Chandra's publications. He found
that raising CO 2 concentration to 700
ppm resulted in an instantaneous
increase in photosynthetic
productivity of 38-48 per cent,
depending on strain. Unfortunately,
his work doesn't discuss the effects
of CO 2 fertilization at concentrations
higher than 750 ppm.
As CO 2 concentrations are
increased well above ambient, the
law of diminishing returns applies
to the benefits. This means that the
degree to which additional CO 2
increases productivity drops as ppms
increase, ultimately reaching the
point at which plant stress occurs.
As with most things, too much CO 2
can have negative effects, leading
to lower yields and leaf death at
extremely high levels.
The concentration at which CO 2
becomes detrimental to plant health
varies widely between species.
Tomatoes, for example, have an
upper threshold of about 2,000 ppm,
while chrysanthemums experience
stress at concentrations greater
than 1,200 ppm. In the absence of
research to clarify the issue, my
view is that our favourite plant
likely falls on the higher side of
the continuum, as cannabis is a
highly productive annual capable
of explosive growth.
Another consideration is that,
over time, many C3 plants fail to
maintain the productivity gains that
they initially experience with CO 2
fertilization. Understanding this
goes back to RuBisCO activity.
Scientists studying the phenomena
have found RuBisCO levels in many
plant species lowers over time in
response to elevated CO 2. This
occurs because the environmental
cues that drive RuBisCO production
are suppressed under enhanced
CO 2 conditions. The degree to
which acclimation to enhanced
CO 2 occurs is species-specific, and
few studies have evaluated this
response at CO 2 levels higher than
700-800 ppm. In cannabis, it may be
more effective to gradually increase
CO 2 concentrations over the crop
cycle, as opposed to raising them to
the highest level immediately.
As cannabis legalization continues to
progress and the markets in legal states
mature, the physiology of cannabis will
hopefully be studied to the same degree
as other crops. With these efforts will
come a better understanding of how to
best use CO 2 fertilization in cannabis
cultivation. Until that time, my advice
is to enhance bloom in the 1,200-1,600
ppm range, with 1,400 ppm as a good
rule of thumb. If you are running CO 2
in the vegetative phase, I don't recommend
exceeding 800 ppm. This level
provides your vegetative plants with
a good boost and ensures that they
see a significant benefit as they move
into higher CO 2 in flower. If able, I also
recommend experimenting with different
levels of CO 2 fertilization and with
gradually increasing CO 2 concentrations
across the bloom cycle.
Daniel Banks is a consultant and
passionate cannabis enthusiast based
in Denver, Colorado. He completed
a bachelor's degree in Horticultural
Science and a minor in Entomology at
Colorado State University in 2012. His
company, Next Generation IPM LLC,
provides Integrated Pest Management
focused consulting to licensed
cannabis cultivators.
“CO 2 FERTILIZATION
ALLOWS cannabis
to thrive at higher
temperatures and
utilize higher light
intensities, but these
two factors need to be
considered together.”
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