Silica – Sesquioxide ratio

The proportion of silica to sesquioxides in the clay fraction of soil expressed as a molar ratio, It may be about 6.0 in the original rock and range from 1.25 – 3.6 in most soils.

The ratio is high in clayey soils and low in coarse light soils. A high ratio means high base exchange, hygroscopic and field moisture capacity and fertility in general.

Soil types Silica-sesquioxide-ratio
Black soil 3.0-4.3
Black soil >2.5
Red or brown soil 2.0-2.5
Laterite soil <1.33