SILICON FERTILIZERS: AGRICULTURAL AND ENVIRONMENTAL IMPACTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 186

Note: D - dissolving, Pr - precipitation, P -polymerization, Dp - depolymerization, Dh -
dehydratation, S - salt formation, R - replacement of inorganic anions, Oc - formation of organo-
silicon compounds, Ns - formation of complexes with inorganic compounds, Os - formation of
complexes with organic compounds, Dc - decomposition of complexes, M - mineralization of
organo-silicon compounds.
Figure 1. Silicon cycle in system soil-plant-microorganisms (Biel et al., 2008).
Except mono-, oligomers and polysilicic acids, organosilicon compounds are present in
soil, water systems, and living organism tissues (Voronkov et al., 1978). The occurrence of
organosilicon substances and their classification is discussed now.
Soluble Si-rich substances play an important role in the soil-plant system because of their
high biogeochemical activity. There are monosilicic acid, polysilicic acid, organosilicon
compounds, and soluble complexes with organic and inorganic compounds. Monosilicic acid
is topping soluble Si-rich substance of a soil. Monosilicic acid is adsorbed by plants and
microorganisms (Yoshida, 1975). The soil solution monosilicic acid is responsible for the
trend of transformation of secondary minerals and concentration of mobile P, Al, Fe, Mg, and
Mn (Lindsay, 1979; Matichenkov et al., 2011). Monosilicic acid controls formation of
polysilicic acid and organo-silicon compounds in soil and living organisms (Mann and Ozin,
1996; Matichenkov and Bocharnikova, 1994).
At our Planet, biological cycle of silicon is the most intensive in terrestrial ecosystems
where plants uptake silicon in the range from 20 to 7000 kg Si/ha/year (Matichenkov and
Bocharnikova, 1994). Silicon is the 4th most abundant element in plant biomass after oxygen,
carbon, and hydrogen (Bazilevich, 1993; Knight and Kinrade, 2001; Perelman, 1989). As
noted above, the plants and soil microorganisms are able to uptake only monomers of silicic
acid and its anions (Ma, 2003; Yoshida, 1975). In higher plants, this process takes place