SILICON FERTILIZERS: AGRICULTURAL AND ENVIRONMENTAL IMPACTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 188

Mechanical

The accumulation of Si in the epidermal tissue creates mechanical plant protection.
Absorbed molecules of monosilicic acid are accumulated in the epidermal tissues (Yoshida,
1975; Figure 2) and form the silicon-cellulose envelope where silicon is bonded with pectin
and calcium (Ma and Takahashi, 2002). As a result, the double cuticle layer protecting and
mechanically strengthening the plants is formed. The mechanical protection of plants against
biotic (fungi and insect attack) and abiotic (lodging) stresses is probably the most investigated
and popular for explanation of Si fertilizer direct effect on plant resistance.

Physiological

The physiological effect of Si on plants proceeds via the formation of better developed
root system (Kulikova, 2012; Ma and Takahashi, 2002). Monosilicic acid supports stability of
chlorophylls molecules and other organelles which reinforce physiological plant stability
(Biel et al., 2008; Matichenkov et al., 2008; Snyder et al., 2006). We suggested that
increasing of plant drought tolerance by soluble Si realized via physiological mechanism. Due
to high concentrations found in the symplast and apoplast of plant, polysilicic acid can keep
water and its molecules can serve as a rechargeable water tank (Matichenkov et al., 1994). As
shown in greenhouse and field tests, Si fertilization makes possible to reduce water iirrigation
application rate by 30-40% without reduction in the yield (Table 1).

Chemical

Salt toxicity is a worldwide agricultural problem. Approximately one-third of the world
land surface is arid and semi-arid, of which half is affected by salinity. In the nearest future,
under global warming, the problem will increase. Several hypotheses were proposed to
explain the beneficial effect of active Si on the plant salt tolerance. They are (i) improved
photosynthetic activity, (ii) enhanced K:Na selectivity ratio, (iii) increased enzyme activity,
and (iv) increased concentration of soluble substances in the xylem, which results in reduced
sodium adsorption by plants (Biel et al., 2008; Matichenkov and Bocharnikova, 2001; Snyder
et al., 2006).

Table 1. The effect of Si fertilizers on the weight of 3-week old wheat
and the content of active Si in Chestnut Soil

Treatment Optimum moisture Water deficiency (50%)

Dry weight
(g)

Active Si
(mg/kg)

Dry weight (g) Active Si

(mg/kg)

Control 0,33 8,45 0,20 6,32

SiO 2 1000 kg/ha 0, 42 18,62 0,31 18,41

Deatomitoes earth 1000 kg/ha 0,38 14,70 0,32 12,32

Monosilicic acid, 100 mg/l Si 0,37 12,82 0,28 11,24

LSD 05 0,04 0,62 0,03 0,56

Matichenkov et al., 2011.