O HORIZON
SURFACE LITTER:
fallen leaves and
organic debris
Litter
L
F
Partially
decomposed
litter
A HORIZON
TOP SOIL:
organic matter (humus),
living organisms,
inorganic minerals
E HORIZON
ZONE OF LEACHING
(ELUVAL HORIZON):
dissolved or suspended
materials move
downward
B HORIZON
SUBSOIL:
accumulation of iron,
aluminium, humic
compounds and clay in
illuval horizons leached
down from the A and E
horizons; more altered
material than in C horizon
C HORIZON
WEATHERED PARENT
MATERIAL:
partially broken-down
inorganic minerals
R HORIZON
BEDROCK:
impenetrable layer
Fresh
M
Fig. 4.21Idealized soil profile showing master soil horizons and horizon abbreviations. The
O, A, E and B master horizons can be further subdivided into subordinate horizons depending
on composition (see Figs 4.23–4.25). Note that the O horizon is composed of fresh (L) and
partially decomposed (F) organic litter. Soil profiles are typically 0.5–1.0 m thick such that
master horizons are typically centimetres to tens of centimetres thick. SOM, soil organic
matter; CEC, cation exchange capacity.