SILICON FERTILIZERS: AGRICULTURAL AND ENVIRONMENTAL IMPACTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 193

traditional methods used to regulate and manage HM mobility in the soil, such as changing
pH or increasing soil adsorption capacity by adding amendments to the soil, are not so
effective because of constant change of the soil matrix, caused by the action of plants,
microorganisms, and inflow and outflow of water solutions (Kavamura and Esposito, 2010).
Many researches have showed that Si fertilization provides reduction in the heavy metal
mobility in the soil and plant protection against heavy metal toxicity (Cunha et al., 2008;
Matichenkov, 2008; Treder and Cieslinsky, 2013).
Si in Sustainable Agriculture
In cultivated soils, the balance of nutrients is usually destroyed through their annual
harvesting with crop. The Si removal from cropland ranges from 40 to 300 kg Si ha -1
(Matichenkov et al., 2011). Increasing Si deficit causes a number of negative consequences
for soil and plant. The lack in soluble Si leads to accelerating soil degradation processes
manifested as reduction of soil organic matter, decreasing water-holding and adsorption
capacities, increasing the Al toxicity. Insufficient plant-available Si in the soil negatively
impacts natural plant defense system against biotic and abiotic stresses (Biel et al., 2008;
Matichenkov et al., 2011).
At present, the Si fertilizer requirements of the world agriculture are estimated to reach
about 700 mln. t. The major problems concerning the Si fertilization are scanty information
being disseminated on the benefits of using Si-rich materials as a fertilizer and absence of
highly informative Si soil tests to assess the plant-available silicon deficiency.
Si Soil Test
The absence of simple, universal, and informative methods for soil classification on the
deficiency of plant-available and active forms of silicon retards practical use of Si fertilizers
in the world. The large number of methods of soil testing for plant-available Si have been
suggested, they differ in the preparation of the soil samples, type of extractant, procedure of
the extraction, and the method that is used for the determination of Si in the extract
(Matichenkov, 2007). A serious problem with regard to all methods is the treatment of soil
samples prior to analysis. During soil drying, both poly- and mono-silicic acids transform into
silicon dioxide, as a result, data obtained on dried soil may not adequatly describe plant-
available soil silicon. We offered to determine monosilicic acid (plant-available Si) in water
extract from fresh soil sample. To describe Si nutritional status of a soil, an analysis of
monosilicic acid is not enough. Monosilicic acid is an active form of Si controlling the Si
plant nutrition and primary soil biogeochemical processes. This is ‗actual Si' which exists in
the soil solution at the moment. Besides actual Si, it is necessary to have information about
soil Si compounds that can be transformed (dissolved) to actual form in the future. This is
‗potential Si' . The potential Si may be determined by the hydrochloric acid (0.1 n) -
extraction method from dry soil.
In practice, to evaluate the silicon nutritional status, united parameter is more suitable.
Such complex parameter can be described as ‗active Si'.