Soils in their environment - Fundamentals of the Physical Environment - page 437

INCREASING PRECIPITATION

South North

Soil names
FAO CHERNOZEMIC SOILS LUVISOLIC SOILS

Dark
brown

Dark
grey

Canadian Brown Black Grey wooded soil

cm

HUMUS
HORIZONS

30

60

Calcium
Carbonate
CaCO 3

90

Gypsum
CaSO 4 .2H 2 O

120

Figure 18.7 Lime and gypsum horizons of deposition in a transect of increasing precipitation from south to north in the
Canadian prairies.

expect, the most distinctive podzol profiles are found
where drainage is good and the parent material is acid, as
on acid igneous and metamorphic rocks, sandstones and
depositional acid sands.
Most soil classifications recognize different types of
podzol, depending on local conditions ( Figure 18.8 ). The
typical humo-ferric podzol (FAO: Orthic Podzol) has
accumulations of organic material (Bh or Bhs) overlying
the horizon of iron accumulation (Bs) ( Plate 18.10 ). This
is the normal profile found under coniferous and mixed
forest in Russia and North America where the parent
materials have a moderate content iron content. They are
common on coarse, non-calcareous rocks or on superficial
materials like glacial tills from which free lime has been
removed. By contrast, humus podzols have well developed
Bh horizons but lack any horizon of iron accumulation.
They form under cool, moist conditions, usually on parent
materials with a low iron content ( Plate 18.1 ).

Plate 18.9 Iron Podzol (FAO: Ferric Podzol) in fluvio-glacial
sands beneath white spruce in the Canadian boreal forest.
Litter and fermentation layers (L and F) overlie the white
eluvial horizon (Ea) and the orange-brown illuvial horizon (Bs).
Photo: Ken Atkinson