Fractionation of iron and manganese in the horizons of a nutrient-poor forest soil profile using the sequential extraction method.

Abstract

Soil iron and manganese fractionation is evaluated in the soil profile sampled from a pine-covered area of Wielkopolski National Park (mid-western Poland), that for years has been exposed to acid rain. The soils studied are sands and loamy sands with a pH of 3.3-4.4. The content of iron and manganese was analyzed by sequential extraction in the following fractions: exchangeable, acid extractable, reducible, oxidizable, and residual. The soil profile displays a lithogenically dichotomous structure that is reflected in the iron and manganese content, especially in the Fe residual fraction and Mn oxidizable fraction. In terms of the lability of manganese, it can be stated that the amount of manganese in reducible fractions (Mnred) is higher than in exchangeable and acid extractable ones (except in the surface layer), while the amounts of manganese in fractions in which it is poorly available (Mnox) and unavailable (Mnres) are lower than that of Mnred. For iron, this sequence looks as follows: Feex<Feac.ext<Fered, while the amounts of iron in fractions in which it is poorly available (Feox) and unavailable (Feres) are similar and decidedly predominant. The availability of the most readily released iron and manganese lessens with depth, and of the remaining forms grows in accordance with the change in lithology.