Silicon in Soils and Plants

Abstract

The crust of the earth is largely composed of silicon that is found primarily as silicate minerals, secondary alumino silicates and various forms of silicon dioxide. However, the abundance of silicon in soils is not an indication that sufficient supplies of soluble silicon are available for plant uptake. In this chapter, the outcomes of many years of research conducted on silicon are consolidated to understand the state of knowledge for silicon fertilization guidelines in crop production. Monosilicic acid (H₄SiO₄) is the form of silicon used by plants, which is found both in liquid and adsorbed phases of silicon in soils. The concentration of the H₄SiO₄ in the soil solution is influenced by the soil pH and the amounts of clay, minerals, organic matter and Fe/Al oxides/hydroxides, which are collectively related to the geologic age of the soil. Fertilization can rapidly increase the concentration of H₄SiO₄ in the soil solution; therefore, fertilization has become a common practice in areas with intensive cropping systems, particularly for those soils that are inherently low in soluble silicon. The establishment of procedures to estimate the plant-available silicon and the critical soil silicon levels and the method (5-day Na²CO₃-NH₄NO₃ extraction) to analyze the soluble silicon fraction in solid fertilizers were among the advances in research on silicon in agriculture in recent years. These measurements were the key components required for the development and implementation of effective silicon fertilizer management in crop production. However, many aspects of the role of silicon in soil science remain understudied, and these aspects should be the focus of future research.