Loss of soluble substances and colloids from the top layer of soil by percolating precipitation.
The materials are carried downward and are generally redeposited in a lower layer. This transport results in a porous and open top layer and a dense, compact lower layer. In areas of extensive leaching, the remaining quartz and hydroxides of iron, manganese, and aluminum form laterite . In such areas rapid bacterial action results in the absence of humus in the soil, because fallen plant material is oxidized and the products are leached away.