The soil solution composition in soils under natural forest north of Kyoto has been studied to determine whether podzolization is an on-going soil-forming process.
In the eluvial E or A2 horizon of the podzolic soils, Fe and Al occurred in large amount in the soil solution with a low pH which contained a high concentration of dissolved organic carbon (DOC), often associated with a high NO3 content, whereas in the horizons below B1 the amount of Fe and Al was smaller and the pH of the soil solution was high. These observations indicate that the profiles were undergoing an active process of podzolization.
It is considered that the decrease of the pH by H+ originating from DOC dissociation and/or nitrification is indispensable for podzolization. The pH of the soil solution may be the factor which determines the intensity fo eluviation of Fe and/or Al from the A horizons. The soil solution pH per se could also be a factor contributing to the differentiation of podzolic soils from brown forest soils.
On the other hand, along with the increase of the pH of the soil solution in the illuvial Bs horizons, the Fe and/or Al concentration clearly decreased with or without a concomitant decrease of the amount of DOC. This phenomenon indicates that the co-precipitation of Fe and/or Al with DOC did not necessarily occur and that the solubility of Fe and/or Al in the soil solution may be mainly controlled by the pH rather than the quantity of DOC.