ANNEX
I - PHOTOGRAPHS OF SOIL PROFILES
All photographs by courtesy of the International Soil
Reference and Information Centre (ISRIC), International
Soil Museum, PO Box 353, 6700 AJ Wageningen, the
Netherlands.
The international classification of the soil is provided in parentheses,
for information. FAO. 1974. FAO-Unesco Soil map of the world (1:5 000
000), Volume I: Legend. Paris, Unesco.59 p.
|
|
|
|
 |
|
Master horizons and
subhorizons are well defined in this soil profile. There is
accumulation of organic matter in horizons A, B 1 and B 2.
The eluvial E-horizon has a much lighter colour due to leaching
(humic podzol). |
|
|
 |
|
A lateritic soil typical of the humid tropics.
In this case, there has been no ground-water influence within
the 0- to 125- cm zone where there is neither plinthite nor
hard concretions. The B-horizon is a reddish sandy loam relatively
rich in iron salts and with at least 15 percent clay (orthic
ferralsol, Zambia) . See also Photograph 9. |
|
|
|
|
|
 |
|
A deep tropical soil with two well- defined
master horizons, A and B. This last horizon contains enough
clay to reduce its permeability to a reasonably low value
(chromic cambisol, Botswana). |
|
|
 |
|
Freshwater acid sulphate soil developed in a
river plain from recent alluvial deposits. The hydromorphic
conditions are here characterized by conspicuous yellow mottles
in the bottom part of the B-horizon (B2). These mottles are
made of an iron sulphate compound, jarosite, formed through
exposure to the air and bacterial activity from a mineral
containing iron and sulphur, pyrite. The C-horizon is reduced
(thionic fluvisol, Thailand). |
|
|
|
|
|
 |
|
Black cotton soil commonly found in relatively
dry, warm climates. It is characterized by a high content
of very fine clay (montmorillonite), a low content of organic
matter and a very dark colour, sometimes reddish. When dry,
such soils develop cracks from the surface downward; which
at some period in most years are at least 1 cm wide to a depth
of 50 cm. They are called regur in India and tir in Morocco
(pellic vertisol, Botswana). |
|
|
 |
|
Peat soil, with the organic H-horizon formed
or forming from accumulation of organic matter deposited on
the surface, that is saturated with water for long periods
(dystric histosol, Ireland) |
|
|
|
|
|
 |
|
A soil profile showing the influence of ground
water within 50 cm of the surface. The hydromorphic properties
are characterized by mottles in the top part of the B- horizon
(B1) and the dull greyish colour of the reduced part of the
B- horizon (B2). The latter is a sign of drainage trouble
for a good part of the year. The C-horizon is also reduced
(eutric gleysol). |
|
|
|
|
|
|
|
 |
|
The B-horizon is rich in clay. Down from 75
cm, red mottles are made of plinthite. This is a firm, iron-rich
clay which becomes irreversibly hard when exposed to repeated
wetting and drying, forming an ironstone hardpan - see Photograph
9 (plinthic acrisol, Nigeria). |
|
|
|
|
|
|
|
 |
|
A lateritic soil commonly found in tropical
and subtropical climates where dry and humid conditions alternate.
The B- horizon is enriched in clay and in iron salts. Down
from 70 cm, it shows an ironstone hardpan, a continuous rock-like
layer made by irreversibly hardened plinthite where iron compounds
are the primary cementing agents (ferric acrisol, Nigeria).
|
|
|
|
|
|
|
|
 |
|
10. Granular structure
in a B-horizon. |
|
|
 |
|
11. Crumb structure in an A-horizon. |
|
|
|
|
|
 |
|
12. Subangular blocky structure in a B-horizon.
|
|
|
 |
|
13. Prismatic structure in a B-horizon |
|
|
