About variable charges in soil

Variable charge soils are soils that exhibit changes in surface charge based on environmental conditions, pH, and the presence of ions. These soils are primarily found in tropical and subtropical regions and play a vital role in nutrient dynamics and contaminant behaviour. However, young soils such as those derived from basalts including allophonic and imogolitic soils also exhibit variable charge. Old deeply weathered landscapes such as those in southern Australia also exhibit variable charge.

By contrast, the classical soils science textbooks that have influenced a lot of soil science their and applications were written about European and North American soils where fixed charge on clays is the dominant process and less emphasis was given to variable charge soils and their properties.

Key Features:

• Distribution: Predominantly found in weathered regions with high rainfall, including parts of Africa, South America, and Southeast Asia. Less weathered soils that include volcanic/basaltic ash derived soils including Japan, NZ
• Mineralogy: Composed of minerals such as allophanes, imogolites, kaolinite, gibbsite, and oxides of iron and aluminium, which influence chemical retention and release.