SILICON FERTILIZERS: AGRICULTURAL AND ENVIRONMENTAL IMPACTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 187

through the roots and leaves. However, the silicon is distributed within the plant irregularly,
according to the needs of the organism (see below). Cultivated plants annually remove from
soil 30 to 70 kg Si ha -1 (Anderson, 1991; Bazilevich, 1993; Ma and Takahashi, 2002; Savant
et al., 1999). Usually the concentration of monosilicic acid in the soil is ranged from 5 to 40
mg Si L -1 . The removing of these substances results in crushing of the Si biogeochemical
cycle in the arable soil and accelerating the following processes: soil texture degradation, soil
organic matter decomposition, reduction in soil adsorption capacity, reduction in nutrient
plant-availability (Biel et al., 2008; Kulikova, 2012; Matichenkov, 2007, 2008). To restore
soil silicon status, Si fertilizers and soil amendments are necessary.
Silicon fertilization has a double effect on the soil-plant system. Firstly, improved plant
Si nutrition reinforces plant protective properties against diseases, insect attack, and
unfavorable climatic conditions. Secondly, soil treatment with biogeochemically active Si
substances optimizes soil fertility through improved water, physical, and chemical soil
properties and maintenance of nutrients in plant-available forms.
Si Effect on Plants
Silicon is an integral part of plants. Distribution of silicon between plant organs is not
equal and may vary from 0.001% in the pulp of fruit to 10-15% in the epidermal tissue (Ma
and Takahashi, 2002). Plants have a special mechanism for selective uptake of monosilicic
acid from the soil solution (Ma et al., 2006). Plant tissues are characterized by extremely high
concentrations of mono- and poly-silicic acids in the sap and are able to redistribute this
element rapidly inside the plant (Biel et al., 2008). The main function of Si in plant is
formation the defense system. Silicon provides the protective functions of plants on the
mechanical, physiological, chemical, and biochemical levels.
Figure 2. Schematic representation of the rice leaf epidermal cell (Yoshida, 1975).