Characteristics of an acceptable silicon (Si) source are: a high content of soluble Si, physical properties conducive to mechanized application, ready availability, and low cost. Since Si is the second most abundant element in the earth's crust, finding sources of Si is easy. But Si is always combined with other elements and most sources are insoluble. Responses of crops to soluble Si applications in sands (largely SiO₂) provide an example of the insolubility of one source. Slags (by-products) from the processing of iron and alloy industries, have been utilized, their concentrations and solubility of Si and their contents of other elements vary widely. Potassium silicate is used in nutriculture for disease control in some high value crops but are too costly for general use. Sodium silicate and silica gel have also been used to supply Si in research and high value crops.

Calcium silicates have emerged as the most important sources for soil applications. Of those, calcium meta-silicate (wollasonite, CaSi0₃) has been the most effective source in many locations with low concentrations of soluble Si in soils. Such a material, supplied as a slag by-product from the high temperature electric furnace production of elemental P is applied extensively to organic and sandy soils for application for sugarcane and rice crops as well as utilization on turf.