Fe, Al, silica a. silica is dissolved and leached from the soil profile. Fe and Al remain. Oxisols are actually mined for iron and aluminum ore. The deep red color of oxisols is an expression of the iron and aluminum oxides. All the nutrients are tied up in the biomass.
Plants hold nutrients in tissue.
When litter falls, decomposition and leaching are so fast that plant must rapidly uptake mobilized nutrients, or they will be lost from setting. When rainforests are harvested or cleared, nutrients are removed. Soils left behind are impoverished, often dry to brick-like structure. Low fertility for agriculture. C horizon 5.