Problem 2
The weathering of some clay minerals containing potassium is affected by growing plants. Explain why this might be so.
Problem 3
The surface soil in the humid tropics is often depleted in silica and enriched in iron and aluminium oxides. In contrast, the surface mineral layer of a forest soil in a temperate region may be devoid of significant iron and aluminium minerals, and have a high concentration of silica. Suggest an explanation.
