SILICON FERTILIZERS: AGRICULTURAL AND ENVIRONMENTAL IMPACTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 195

Table 5. Effects of zeolite, diatomaceous earth and advanced Si fertilizer on yield of
selected crops (Matichenkov, 2008)

Cultivated
plants

Zeolite Diatomaceous earth Advanced Si fertilizer

Effect, % Rate, kg Effect, % Rate, kg Effect % Rate, kg

Potatoes 62 600 12.9 1000 65 300

Water melon 30.8 300 - - - -

Cucumber 33 825 24.6 2000 82 400

Wheat 42.5 400 - - 55 100

Barley 30 250 - - 52 100

Banana - - 11.7 1000 - -

Sugarcane - - 20.5 1000 - -

Plant remains-based fertilizers or plant ash can be used as silicon sources, however, the
demand for silicon fertilization generally exceeds that which can be supplied by plant
residues. Ones of the most popular and widely used silicon fertilizers are Si-rich industrial by-
products or slags. But they may contain heavy metals , associated with their origin and
processing. The high rates needed to supply silicon may result in heavy metal concentrations
greater than allowed. For example, the application of the slag in Florida (the Everglades
Agricultural Area) resulted in significant increase in the Pb content in sugar produced from
local sugar cane. In spite of ecological control, the use of indu strial slags as Si fertilizers
creates high risk for heavy metal pollution.
The best type of Si fertilizers is natural minerals high in plant-available Si. There are
zeolites, diatomaceous earth, bentonite et al. The major problem with this type of the Si
fertilizers (soil amendments) is a high application rate required. The diversity of rates with
different fertilizer types can be attributed to the different solubilities of silicon compounds.
Table 5 shows comparison effects of zeolite (Khotynetsky deposit, Russia) and diatomaceous
earth (Palkarra deposit, Australia) on plant growth.
The effeciency of the natural Si-rich minerals as Si fertilizers depends on their solubility
and other properties (Kulikova, 2012). To estimate potential value of a source, we suggested
the Si determination in water and weak acid extracts (Matichenkov et al., 2011).

Advanced Si Fertilizer

The main problems in the practical application of Si fertilizers or Si-rich soil amendments

are:

a) low efficiency, as a result, high rates are required (the rates of by-products from
metals industry used as Si source or Si-rich minerals such as diatomite, zeolite or
others range 300 to 6000 kg ha -1 );
b) high cost of Si-rich soil amendments per hectare. For example, natural Si fertilizers
usually have cost 300-600 US$ per ton with application 2 t ha -1 ;
c) a short-term effect of liquid Si fertilizers;