Interesting article on Silicon

[Guest guest]

Thank you !

It's important to note that there's a difference

between silicone and silicon.

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http://www.bmi.net/roseguy/pnw/silicon.html

Northwest rian

The Pacific Northwest District of the American Rose

Society

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Silicon: More than a Nutrient

By Don n

(Originally published, March 2000)

Tissue studies of plants have found more than 60

different mineral elements, although it has generally

been accepted that 17 elements are essential for plant

growth. We are well familiar with the macronutrients

of nitrogen, phosphorous, potassium, calcium,

magnesium and sulfur. Most of us recognize the

micronutrients of iron, manganese, boron, copper,

molybdenum, zinc, chlorine, and more recently added to

the list, nickel (the remaining three elements are

carbon, hydrogen and oxygen). However, studies

periodically explore the roles played by other

elements such as sodium, cobalt, vanadium, lithium,

rubidium, strontium, aluminum, selenium, iodine,

titanium and silver. Many of these elements are

readily available in the soil and used in such tiny

quantities that not much research has been focused on

them beyond identifying locations in the plant and

possible roles in plant metabolism. Only recently have

we begun to explore the possibilities of using these

elements to enhance plant performance. For example,

siler blocks the action of ethylene, which causes

flower petals to wilt; the life of cut flowers can be

extended 100% if pretreated with silver compounds.

The most interesting and promising research is in the

role of silicon. This element is readily available in

the soil; silicon is the second most abundant element,

after oxygen, present in the earth’s crust as silicon

dioxide (sand) and various silicates. Sheet silicates

are compounds of silicon, oxygen, metals and

carbonates arranged in crystalline structure and often

include aluminum, iron, titanium, magnesium, calcium,

lithium, manganese, sodium, and potassium in varying

compositions. Hundreds of sheet silicates occur in the

crust, providing a smorgasbord of mineral nutrients,

but all serving as a ready source of silicon.

Silicon extracts from sheet silicates as silicic acid.

Soil water generally contains 50 to 400 ppm silicic

acid, which is readily absorbed by plants. Studies of

plant tissue have found a range of silicon content

from a fraction of 1% dry matter to as high as 10%. In

plants, the silicon seems to play a role in growth,

mineral nutrition, mechanical strength, resistance to

fungal diseases, and reaction to adverse chemical

conditions.

Silicon is transported from the roots to shoot through

the transpiration stream and deposited either as

hydrated silicon dioxide or as silica gel or

polysilicic acid (a little disagreement here). Once

the silicon is incorporated into tissue, it doesn’t

move, so a regular supply is necessary.

Silicon affects the absorption and translocation of

several macro- and micronutrients. It also contributes

to the strength and thickness of cell walls, helping

to keep plants erect and resisting attacks by fungi

and insects. Silicon also plays some role in helping

the plant survive adverse conditions such as high

salinity or toxic levels of manganese, iron,

phosphorous and aluminum.

Hydroponics growers have practiced adding soluble

silicon to growing solutions using potassium

metasilicate or sodium silicate, finding that it

reduces the incidence and severity of powdery mildew.

Recent hydroponic trials in New Zealand found that

raising the silicon concentration increased yields and

produced thicker, whiter, healthier root systems.

In our experience as rosarians, we’ve seen that roses

do well in a somewhat clay soil. We recommend that

garden soil be added to container culture instead of a

soilless mix. We’ve made the assumption that clay is

good because it holds water well and has many more

sites for ion exchange. We’ve assumed that adding

garden soil introduces microbiota into a container

mix. These assumptions are probably still valid but

may not be the complete answer; clay…essentially a

sheet silicate…provides silicon as well.

The importance of silicon in plant nutrition is

perhaps interesting by itself, but of more interest

are recent studies regarding silicate applied as a

fungicide. Studies at the Pacific Agri-food Research

Centre (PARC) in British Columbia first explored the

powdery mildew control and increased yield by adding

silicate to growing media, but continued to explore

silicate sprays, in a form currently used as a food

additive, finding good control of powdery mildew on

grapes, melons, zucchini, cucumber. Continuing study

reveals that the form of silicon in solution and the

solution pH greatly affect the efficacy.

At this point, silicon’s mode of action is not

completely understood. In healthy cucumber plants,

silicon accumulates at the base of leaf hairs. When

the powdery mildew spore attempts to penetrate the

leaf, silicon is deposited at the site of infection.

Silicon apparently stimulates the production of

anti-fungal compounds called phenolics that halt the

infection process.

The most interesting result of this study is that Rohm

& Haas chose to formulate Nova (now Systhane, Rally &

Eagle), containing 40% myclobutanil as active

ingredient, with 60% silicate as a carrier (Aluminum

and potassium silicates are List 3 Inert Ingredients).

At this point, it is unknown how much of Nova’s

effectiveness is due to the silicate. It is mindful

that we recommend Immunox to beginning rosarians as

having the same effective active ingredient as

Systhane, Rally and Eagle, but we don’t know if the

inert ingredient is silicate.

Foliar sprays of silicon have also been shown to

reduce aphid populations on field crops.

So where do you get it? Potassium silicate is

available in concentrated solutions from hydroponics

suppliers, although their focus is on adding it to a

nutrient solution. Dyna-Gro Pro-Tekt is a potassium

silicate product offered for solution, soil and foliar

application and sold through hydroponics, bonsai and

orchid supply houses; Dyna-Gro also advertises

Pro-Tekt in American Rose. Pyrophyllite clay is an

aluminum silicate product in powder form that can be

applied as a dust or foliar spray, and available under

a number of brand names (Seaclay, Mineral Magic,

Pyroclay).

For soil applications, consider adding greensand,

which contains glauconite, an iron-potassium silicate

mined from marine sediments in New Jersey. It is a

widely available as a trace elements amendment and

conditioner for soils and potting mixes. Zeolite is

another category of amendments, essentially aluminum

silicates, mined from volcanic and sedimentary

deposits and noted for their absorptive abilities;

clinoptilolite is a zeolite of use in horticulture,

also containing potassium, calcium, magnesium, iron

and traces of manganese, tin and sodium oxides, and

marketed under various brand names, including EcoSand,

Clino-Lite and ZeoPro.

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Copyright 2000, Don n, .

18402 100th Ave SE, Snohomish WA 98296-8038

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