Home' Grower : September 2012 Contents The South Australian Grower – September 2012
plant cell wall
Silica neglect costly
❏ By JOHN NORTON
AMAJOR mineral is missing
in many soils and most soil
tests do not even monitor its
This mineral is silicon.
It can increase stress resistance,
boost photosynthesis and chloro-
phyll content, improve drought
resistance, salt tolerance and soil
fertility, and prevent lodging.
Science is rapidly revealing the
scope and scale of our silicon neg-
lect. How can the second most
abundant mineral on the planet be
in shortage? That’s because plants
take up silicon as silicic acid and
that is what is missing in the soil.
Something we have done in con-
ventional agriculture appears to
have compromised the conversion
of insoluble silicon into plant-avail-
It may reflect a mineral imbal-
ance or we may have knocked out
some of the soil microbe species
that solubilise this mineral.
A healthy, disease-suppressive soil
should contain 100 ppm of mono-
silicic acid – as measured in a soil
Cell strength is resilience
The plant cell wall is a substantial
barrier that must be breached by
disease to gain access to the good-
ies within. If we strengthen that
cell wall so the hyphae buckle, the
disease cannot gain a foothold.
Many published papers have now
confirmed the exciting potential
for increased disease and insect
resistance through good silicon
Soluble silicon used as a soil
drench was shown to have the
equivalent inhibitory effect as
phosphorus acid in the manage-
ment of phytopthora in avocados.
It was also shown to offer effective
management of dreaded black
sigatoka in bananas, brown rust in
sugar cane, powdery mildew in
cucurbits, fusarium wilt in pota-
toes and leaf blast in rice.
There is a problem here, though.
Silicon is immobile once incorpo-
rated into the cell wall and there-
fore, must be in constant supply.
There are two types of stress that
affect production – abiotic stress is
the negative impact of environmen-
tal factors on living organisms and
biotic stress is about pest pressure.
Abiotic stress is the single most
harmful factor impacting crop
growth and productivity and glob-
al warming is only making it
Biotic stress is not far behind.
Every year since we began the
chemical experiment in agricul-
ture, there has been an increase in
the total amount of chemicals
applied on a global scale, and every
year there has also been a marked
increase in pest pressure.
Silicon can reduce the impact of
both abiotic and biotic stressors.
The stronger the cell wall, the
more stress-resistant the plant,
whether that stress is from
pathogens or non-living factors.
Recently, silicon has been found
to trigger the production of a suite
of compounds that fuel immunity.
But there’s more
Silicon can also provide a major
fertilising response and substantial
In a paper by J Bernal, involving
research with rice and sugarcane in
Columbia, just 100 kilograms to
200kg of magnesium silicate a
hectare achieved yield increases of
14.63 per cent in sugar cane and
the increases in rice ranged from
21pc to 33pc depending on appli-
Brazilian researchers trialed six
different application rates of potas-
sium silicate on potatoes and
found the 1pc rate was most effec-
tive. In fact, 6 litres of potassium
silicate in 600L of water, sprayed
each week during the crop cycle,
produced an impressive yield
increase of 22.4pc.
M. Lynch, a champion of silica
fertilisers in Australia for more
than a decade, presented a paper at
the SA conference where he sug-
gests silica fertilisers have consis-
tently outperformed high-analysis
fertilisers in cereal production.
An avocado grower from North
Queensland found he no longer
lost up to 15pc of his crop to wind
abrasion. The increased skin
strength created fruit that did not
mark when the fruit r ubbed against
the branches in windy conditions.
Silica fertilisers are available in
liquid and solid form and the liq-
uids offer the most rapid response.
Silicon is found in good levels in
rock mineral fertilisers and in rock
phosphate and guano products.
But this is not the plant-available
form of the mineral and may take
many years for the mineral to
Diatomaceous earth in the amor-
phous form is a ver y rich source of
insoluble silica. The material is basi-
cally the exoskeletons of tiny pre-
historic creatures called diatoms.
These remains contain up to 85pc
silica dioxide and the silica shell is
sharp and jagged under a micro-
scope, almost like a broken razor
blade. Diatomaceous earth has
been used as a natural insecticide
for decades, as the jagged, little
razor blades can cut up the offend-
ing insect’s exoskeleton, causing
the creature to dehydrate and die.
This material is also used inter-
nally as a natural means to control
intestinal parasites. The rich silica
lode from diatomaceous earth can
be made plant-available by micro-
nising the material right down to a
tiny particle size of 5 microns. It
can then be held in a liquid sus-
pension and applied via boom
spray or fertigation.
As little as 5L of liquid,
micronized diatomaceous earth a
hectare, applied through fertiga-
tion on a regular basis, can lift leaf
levels of silica into the luxury zone,
with all of the associated benefits.
Potassium silicate is a good solu-
ble form of silica but it is not com-
patible with many other fertilisers
and must often be applied as a
standalone or with boron. One
way out of this limitation is to use
a pre-formulated potassium sili-
cate-based fertiliser which includes
Silicon is an essential pre-requi-
site for proactive pest and stress
management and should be an
integral part of every good nutri-
Liquid silica can be applied with
alkaline materials but definitely not
We suggest using these products
with seaweed powder which
improves the effect on photosyn-
thesis and supplies many other
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