Silicic Acid
Written by Tom Forrest #TomForrestCF
@ TomForrestCF
THE MORE YOU KNOW - THE BETTER YOU GROW
The new hydroponic superstar?
Silicon (Si) is the second most abundant element present in the earth’s crust. Soils generally
contain up to 40% silicon (Kovda 1973) and plants use this key element in vast amounts. Recent
advancements in the production of silicon fertiliser compounds and manufacturing techniques
are allowing for a new wave of silicate products available to farmers.
The physically and chemically active Si substances in the soil are represented by monosilicic
acids, polysilicic acids, and organosilicon compounds (Matichenkov and Ammosova, 1996).
These forms of silicon are interchangeable with each other, as well as with other crystalline
minerals and living organisms (soil microbes and plants). Silicic acid is the general name for a
family of chemical compounds containing the element silicon attached to oxide and hydroxyl
groups.
Monosilicic acid (H4SiO4) is the centre of these interactions and transformations. Monosilicic
acid is the product of silicon mineral dissolution (Lindsay 1979). Monosilicic acids are absorbed
by plants and living organisms (Yoshida 1975). Monosilicic acids can influence soil chemical
and biological properties including significant interactions with phosphorus, aluminium, iron,
manganese and other metal mobility, alongside the stability of soil organic matter.
Monosilicic acid is also essential in the formation of polysilicic acids and secondary minerals,
however plants and microbes can only absorb monosilicic acid (Yoshida 1975). Polysilicic acids
are not immediately absorbable by the plant, however they will influence soil texture, water
retention, cation exchange capacity, and soil erosion stability (Matichenkov et al, 1995).
Modern agricultural research and manufacturing in Europe has developed novel methods of
blending and isolating these silicic acid compounds in a stable form (with a lengthy shelf life;
essential for successful product development!). Products such as SuperSi are now available
worldwide with extremely high concentrations of silicic acids. These are now being successfully
used in the hobby, research and commercial protected cropping industries.
There is ongoing debate about the efficacy of mono-silicic acid products vs older potassium
silicate products. The benefits of silicic acid products over typical potassium silicate products are
easy to explain. Silicic acid products (such as Super Si) contain just that: an absorbable form of
silicic acid. Potassium silicate is a molecule that does not contain silicic acid, but silicate (SiO2),
which is not readily available for plants. When dissolving potassium silicate in water, the silicate
does not dissolve into water soluble silicic acid.
Some people disagree on this topic, but scientists agree that for horticultural purposes the
amount of silicic acid that is yielded from dissolving potassium silicate into water is almost
non-existent. So, to conclude: potassium silicate products are not able to add silicic acid to your
plants’ diet. Much like crude oil versus petrol, silicates must be “refined” before they can be used.
This might however not be a problem, because it is elemental silicon that plants need (not silicic
acid per se). I will elaborate on this in the next paragraph.
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