Podsolisation is an extreme form of leaching which causes the eluviation of iron and aluminium sesquioxides.
The process generally occurs in areas where precipitation is greater than evapotranspiration.  The minerals are removed by a process known as leaching.
When organic material is broken down nutrients are released, but at the same time organic acids are released. These organic acids are known as chelating agents. Many podsol soils form underneath coniferous forests, the fact that pine trees are evergreen causes a very thin litter layer inhibiting the production of humus. As a result, an acidic (pH 4.5) mor humus is produced which provides a greater amount of chelating agents.