Podzol formation in sandy soils of Finland

Podzolization occurs quickly in acidic parent materials with addition of acidic litter from coniferous trees. This study was conducted to evaluate Podzol formation and estimate lengths of time required to meet morphological and chemical criteria of podzolic B horizon and spodic horizon in Finland. Soil color, organic C, ODOE, and extractable Al and Fe were measured in a seven-pedon chronosequence (230–1800 years) and four older pedons (8300–11,300 years). The bulk mineralogical composition of the BC and C horizons was uniform with quartz, plagioclase and K-feldspar as main components and amphibole, illite and chlorite as minor components. The fine (<5 μm) fraction of selected samples was primarily amorphous allophone-like material with some mixed-layered illite–vermiculite. All pedons in the study met the criteria for albic horizons according to the FAO–Unesco, World Reference Base (WRB) and Soil Taxonomy systems. According to the FAO–Unesco system, all pedons had spodic B horizons and were classified as Podzols. According to the WRB system, none of pedons of the chronosequence had spodic horizons, whereas the older pedons met the criteria for a spodic horizon. About 4780 years were required to form a spodic horizon according to the WRB system. The oldest pedon of the chronosequence and the older pedons had spodic horizons according to Soil Taxonomy, but the younger pedons failed to meet the spodic horizon criteria. About 1520 years were required to form a spodic horizon that met the color and organic C criteria of Soil Taxonomy, whereas it took about 4780 years to meet the required accumulation of Fe and Al. This study points out the discrepancy between the color criteria and the criteria reflecting the accumulation of Al, Fe and organic matter in the B horizon.