Silicon Fertilizers

Although silicon is a very abundant element, for a material to be useful as a fertilizer, it must have a relatively high content of silicon, provide sufficient water-soluble silicon to meet the needs of the plant, be cost effective, have a physical nature that facilitates storage and application, and not contain substances that will contaminate the soil (85). Many potential sources meet the first requirement; however, only a few meet all of these requirements. Crop residues, especially of silicon-accumulating plants such as rice, are used as silicon sources either intentionally or unintentionally. When available, they should not be overlooked as sources of silicon. However, the crop demand for application of silicon fertilizer generally exceeds that which can be supplied by crop residues.

Inorganic materials such as quartz, clays, micas, and feldspars, although rich in silicon, are poor silicon-fertilizer sources because of the low solubility of the silicon. Calcium silicate, generally obtained as a byproduct of an industrial procedure (steel and phosphorus production, for example) is one of the most widely used silicon fertilizers. Potassium silicate, though expensive, is highly soluble and can be used in hydroponic culture. Other sources that have been used commercially are calcium silicate hydrate, silica gel, and thermo-phosphate (85).