Geoscience Reference
In-Depth Information
12
Gleysols, Stagnosols and
Histosols
INTRODUCTION
Soils affected by excess water are firstly, Gleysols, from the Russian
gley
, meaning muddy mass; they cover about 720 million ha globally.
Secondly, they include Stagnosols, from the Latin
stagnare
, indicating
submergence. These soils represent 150-200 million ha, according to
FAO. Last come Histosols, from the Greek
histos
, meaning tissue and
indicating, by extension, 'plant fibres'. They cover 320 million ha in the
world.
Excess water induces processes that will be discussed first. Then we
shall study in detail the principal soils and environments affected by
those processes.
12.1 OXIDATION-REDUCTION PHENOMENA
12.1.1
Excess Water and Lack of Oxygen
Excess water because of poor external drainage.
Excess of this kind is seen,
for example, in depressions that collect water and in which natural
drainage is deficient.
Excess water caused by poor internal drainage
. Even when excessive
rain is not received (flat areas), one sees soils in which water stagnates
for long in the humid season because they have a fine-textured (clay),
poorly structured B horizon. These soils have a 'perched water table' in
winter, for example, old fluviatile terraces (Chap. 8).
Causes of excess water
