Abstract
The processes involved in Spodosol (Podzol) formation are still being debated. The pedogenic processes in a Spodosol, 10,700 years-old, at Sotkamo that has been cultivated for about 50 years were studied by characterizing the morphology and analyzing the major chemical properties, texture and mineralogy. Before cultivation, organic acids produced by decomposition of organic matter from pine litter in O and A horizons had weathered primary minerals in A and E horizons releasing Al and Fe. Percolating waters moved the organo-metallic complexes from A and E horizons to Bhsm and Bs horizons where the complexes coated and bridged sand grains eventually forming cemented ortstein. Because of the high biotite content of the parent material, the index of accumulation of Fe and Al in the Bhsm horizon (Al + 0.5 Fe = 4.1%) was the highest reported in Spodosols of Finland. The data support the theory of downward movement of Al and Fe as organo-metallic complexes with formation of some ferrihydrite but little or no formation of imogolite type materials. Little, if any, podzolization has likely occurred since the initiation of cultivation because, after agricultural liming and consequent increase of pH in the Ap horizon, organic compounds are likely to chelate Ca and Mg rather than Al and Fe.;
Highlights
Spodosols (Soil Survey Staff 1999) or Podzols (FAO 1988, 1998) are an extensive group of soils in Finland, other Nordic countries and northern Russia, especially in sandy parent materials and glacial till
The sandy over loamy pedon had a typical Spodosol morphology with a gray colored E horizon and dark, reddish brown colored B horizons (Fig. 1, Table 1). This color pattern suggests organic matter, Al and Fe have been translocated in this pedon from the surface horizons to subsoils where in the Bhsm they have cemented the sand grains together into ortstein
Firm chunks of 2.5YR 2.5/2 ortstein were present in the Bs horizon indicating elevated levels of organic C, Al and Fe have accumulated in these parts of the Bs horizon
Summary
Spodosols (Soil Survey Staff 1999) or Podzols (FAO 1988, 1998) are an extensive group of soils in Finland, other Nordic countries and northern Russia, especially in sandy parent materials and glacial till. A combination of the two theories has been proposed to explain formation of Spodosols in Nordic Countries (Gustafsson et al 1995, Lundström et al 2000) In this combination decomposition of organic matter in O and A horizons produces organic acids that weather primary minerals (Lundström et al 1995, Raulund-Rasmussen et al 1998) in A and E horizons thereby releasing Al, Fe, Ca, Mg, K, and P. Microbial degradation of the organic portion of some complexes in Bhsm and Bs horizons caused some Al and Fe to precipitate as imogolite type materials and ferrihydrite, respectively, in some Nordic soils (Gustafsson et al 1995). As more organo-metallic complexes accumulated in B horizon the coatings and bridges got thicker eventually cementing sand grains into ortstein
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