Soil Formation: Weathering processes and products in the humid tropics

Chemical weathering - end point is clay sized particles

Types:

• Chelation - chemical incorporation, High levels of chelation enable soils to trap nutrients for examples in humus. Deficiency for plant absorption.

• Hydrolysis - exchange reaction involving minerals and water; dissociation of hydrogen ions. After rain, H+ ions go into solution and become magnetically attached to the soil therefore letting other minerals go.

• Reduction - in a saturated environment there are no free oxygen ions. Changes to mobile and immobile iron particles. E.g. below the water table saturation and reduction occurring, above aeration and oxidation - iron rich. 

• Hydration - absorption of water to a chemical compound e.g. during the conversion of hematite to limonite.

• Carbonation - dissolving of carbon in water.

• Solution - clay has slight positive charge therefore able to hold cations (+ve ions). When soil particle has small volume of water surrounding it e.g. after it rains, water around the particle expands allowing cations to drift out into solution. This decreases the strength of the magnetic bonds holding them to the soil.

• Oxidation - reaction of oxygen with minerals causing rusting (product is red soils). High abundance of iron and aluminium ions remain, others lost or 'knocked out'.

…