Sun. 7/12 2:30 PM - Knowledge Center
Silicon - A Beneficial Element
Jennifer Boldt
7/9/2015
What is silicon?
Silicon:
A Beneficial Element
OH
HO – Si – OH
Jennifer Boldt
Research Horticulturist
USDA-ARS, Toledo, OH
OH
Silicon dioxide (SiO2)
Classification of silicon
• Field soils are becoming more highly
weathered
• Highly weathered soils contain less Si
• Applying Si to these soils helps increase
yield and reduce lodging
• In greenhouse production
• The use of soilless media greatly reduces
Si
• Water treatment also reduces background
Si levels
• Therefore, we have unintentionally limited
Si exposure/supply to greenhouse crops
Si benefits:
Powdery mildew suppression
Potential benefits of Si
Improved growth and yield
Larger, thicker stems
Reduced incidence of lodging
Larger flowers
Earlier flowering
More flowers
Enhanced disease resistance
Stress tolerance
Silicone
Why more emphasis on Si recently?
• Beneficial element
• Plant-available form is
silicic acid: Si(OH)4
• Helps protect plants
during periods of
abiotic and biotic stress
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Silicon
&
Silicic acid
+ Si (56 ppm)
- Si (0 ppm)
Basil ‘Genovese Emily’
3 d at 6 °C (43 °F)
* Not every plant will exhibit the same response, but
almost all plants will show at least one positive response
Zinnia elegans ‘Oklahoma White’
Silicon fertilization SLOWED the progression of powdery mildew on leaves of
zinnia, but did not eliminate it
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Publication of this information, in part or whole, is only
permissible through written permission of the author(s).
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7/9/2015
Tolerance to heavy metal toxicity
Nutrient stress
Sunflower ‘Pacino Gold’
- Si (0 mM)
+ Si
• Sources of copper (Cu) in
greenhouses
• Cu ionization systems
• Fungicides
- Si
• Si supplementation can reduce the
severity of Cu toxicity
+ Si (2 mM)
Frantz et al., 2011
2.5
5.0
10.2
15.5
20.4
ppm P
Nutrient stress
Cold stress
+ Si
- Si (0 mM)
Petunia ‘Bravo Pink’
24
22
Flower number
20
+ Si (2 mM)
18
16
14
- Si
12
10
8
6
4
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
P (mM)
2.5
10.2
* Lower values indicate a higher degree of
plant “stress”
20.4
ppm P
Other reported benefits
Reduces damage due to
3 d at 4 °C (39 °F)
Pepper
‘California Wonder’
“Background” sources of Si
• It’s very hard to get a Si-free
environment
• Salt stress
• Heat stress
• Drought stress
3 d at 4°C (39 °F)
Tomato
‘Early Girl’
• Common sources
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Water source
Soilless substrate
Plant material (seed or cutting)
Pesticides
Source
Si
Ultra-pure water
0.3 ppm
City/“tap” water
1.5 ppm
Recirculated water
1.8 to 4.2 ppm
Ground water
2.5 to 5.0 ppm
Fertilizer
0.8 to 5.3 ppm
Frantz et al., 2009
- Si
+ Si
40 mM NaCl
Neil Mattson
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7/9/2015
Should you provide supplemental Si?
• In some instances, background levels of Si present
in greenhouse systems can be sufficient, especially
if plants are not stressed
• However, we have not seen any negative effects of
Si fertilization
• Therefore, providing additional Si can be thought of
as an “insurance policy”
Sources of supplemental Si
• Substrate components
• Sphagnum peat
• Vermiculite
• Substrate amendments
• Par-boiled rice hulls, miscanthus, switchgrass, coir
• Rice hull biochar
• Steel slag (can also be used as a lime alternative)
• Liquid fertilizers
• Potassium silicate
miscanthus
* Mention of products or companies does not imply any
endorsement or preferential treatment by USDA-ARS.
Comparison of Si plant uptake
0.0842
Fertigation (2.0 mM Si)
Par-boiled Rice Hulls (10%)
1.57
1.57
Miscanthus (10%)
1.45
Wollastonite
1.28
“BF”
0.98
“BOF”
“EAF”
“Caster”
2.09
2.05
0.22
“Debris”
0.22
Delivery of Silicon
Leaf Si concentration (% dry weight)
Material
rice hull
1.4
% Si in
Zinnia leaves
Sphagnum peat moss
slag
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
K2SiO4 supplied in
fertilizer solution
100
10
20
40
60
Amount of rice hull
(composted), as a
percent of total volume
A word of caution when using potassium silicate
• Liquid potassium silicate (ex: Dyna Gro Pro-TeKt) CAN NOT be
mixed in the same stock tank as your standard fertilizer solutions
• Suggested trial rate
• 50 ppm silicon for constant liquid feed
• 100 ppm silicon for weekly drench
• Raises pH slightly (ex: 0.3 pH units)
• Cost about 2 cents per pot over 10 weeks
100 ppm N
200 ppm N
1:16 stock
100 ppm N
1:100 stock
Contributors:
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Jonathan Frantz
Scott Leisner
Wendy Zellner
Jim Locke
James Altland
Neil Mattson
Doug Sturtz
Russ Friedrich
The Edward C. Levy, Co.
200 ppm N
1:100 stock
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