Biosphere

Question 1

For a podsol soil, explain the main conditions and soil-forming processes which have led
to its formation.

Answer 1

Thin, black and acidic humus (pH 3·5–4) produced from the slow
decomposition of coniferous needles and cones and cold climate. (1 mark)
 There is limited bacterial activity caused by the cold climate which results
in the slow formation and hence thin/shallow soil. (1 mark)
 Precipitation is greater than evaporation and/or snowmelt results in the
downward leaching of clays, humus, iron and aluminum resulting in an ash
grey A horizon. (1 mark)
 An iron pan develops in the illuviation zone in the upper B horizon as a
result of the redeposition of iron and this can impede drainage, resulting in
waterlogging and gleying in the B horizon. (1 mark)
 Due to the cold climate present for most of the year, there are few soil
biota to vertically mix the soil, so the horizons are well defined. (1 mark)
 The C horizon parent material is generally of weathered (fluvio) glacial
material with a mixture of particle sizes and shapes. (1 mark)