3.4.1 Specific Processes of Soil Formation
3.4.1.1 The Processes of Adding Mineral
and Organic Materials to the Soil Surface
(Additions)
• Accumulation of organic material on the soil surface
(Littering): This process is responsible for the development of the surface horizon (A1). The characteristics of
this horizon differ from one region to another according
to the type and density of vegetation. Taking into consideration that the vegetation cover in Libya is typically
sparse or absent, the amount of accumulated organic
material in the Libyan soils is considered very small.
However, with the rise in temperature, the decomposition
rates of the organic matter will be very high. Thus, an
Ochric horizon is formed. This horizon is the most
widespread soil surface horizon in the Libyan soils. In the
other regions of the country (i.e., Al Jabal Al Akhdar)
where the distribution of the vegetation cover is relatively
high, lower temperatures lead to the formation of the
organic-mineral horizon called Mollic, which is characteristic of Rendolls.
• Mineral accumulation processes (Cumulization):
These processes include both the accumulation of soil
material by wind and water. In Libya, these processes are
mainly responsible for the formation of sand dunes and
Psamments (which is most widespread in the Libyan
soil). As well as the Fluvents which are formed along
flood plains by alluvial (water-deposited) soils. Also,
these processes lead to a delay in the development of the
soil profile, due to the lack of sufficient time for other soil
formation processes to involve in the development of the
soil profile.
3.4.1.2 The Processes of Loss Mineral
and Organic Materials from the Soil
Surface (Losses)
• Leaching (removal of soluble materials): Leaching is
the removal of soluble materials from one zone in soil to
another via water movement in the profile. These processes include washing the water-soluble salts (e.g., calcium and gypsum) inside the soil profile to a deep depth.
The occurrence of this process requires an adequate
amount of water. Therefore, the complete washing of
these materials from the soil profile is limited in areas that
receive high precipitation rates such as the northeastern
region of the country (i.e., Al Jabal Al Akhdar).
• Erosion (removal of the surface layer): The occurrence
of this process leads to the loss of the soil surface layer
through soil erosion by wind and/or water. These processes
are very active in Libyan soils and lead to a delay in the
development of soil profile. As a result, a (Truncated profile) is formed, and that is what usually happens in the soils
of Xeralfs in the Al Jabal Al Akhdar region.
3.4.1.3 Transfers of Organic and Mineral
Materials Within the Soil Profile
(Transformations)
These processes are similar to the previous processes, but the
materials are not completely lost from the soil profile, rather
they are transported from one place and deposited in another
place within the same soil profile. These processes also need
adequate water, but not the same amount of water needed for
the leaching processes. Such processes are responsible for
the formation of many subsurface diagnostic horizons, and
among these processes are the following:
• The process of transporting the water-soluble salts
from the surface by rainwater: Salts are deposited in
the subsurface layers forming the saline horizon (Salic),
in which the percentage of salts is more than 2% (i.e.,
Salids).
• The process of transporting the calcium carbonate
from the surface by rainwater: During this process,
calcium carbonate is deposited at varying depths
according to the amount of precipitation. This process is
responsible for the formation of the Calcic horizon, the
Petrocalcic horizon, and the Caliche layer, as in the case
of Calcid soils.
• The process of transporting the gypsum (dihydrate
calcium sulfate) from the surface by rainwater: In this
process, gypsum is deposited at different depths,
according to the precipitation rates in the area. This
process is responsible for the formation of the gypsum
horizons (Gypsic or Petrogypsic). These horizons may be
formed by transferring gypsum from the groundwater
level close to the surface, as in some Sabkhas. Usually,
gypsum in this case is below the saline horizon (Salic), as
in the case of the Gypsids.
• The process of transporting the Silicate clay (Illuviation): The process of transporting silicate clay minerals to
the subsurface layers is a water-assisted transport in a
basically vertical direction. First, the hydrolysis process
needs to take place to form secondary clay minerals in the
soil. Thus, this process requires a sufficient amount of
water (high humidity conditions). Therefore, this process
is very rare and occurs in Libyan soils. However, it was
found that the Libyan soils contain the clay horizon
(Argillic) and the Sodic horizon called Natric. Scientists
have indicated that the existence of the clay horizons in
arid soils can be explained by one of the following reasons (Dregne 2011; Ben Mahmoud 1995):
44
K. R. Ben Mahmoud and H. A. Zurqani
3.4.1.1 The Processes of Adding Mineral
and Organic Materials to the Soil Surface
(Additions)
• Accumulation of organic material on the soil surface
(Littering): This process is responsible for the development of the surface horizon (A1). The characteristics of
this horizon differ from one region to another according
to the type and density of vegetation. Taking into consideration that the vegetation cover in Libya is typically
sparse or absent, the amount of accumulated organic
material in the Libyan soils is considered very small.
However, with the rise in temperature, the decomposition
rates of the organic matter will be very high. Thus, an
Ochric horizon is formed. This horizon is the most
widespread soil surface horizon in the Libyan soils. In the
other regions of the country (i.e., Al Jabal Al Akhdar)
where the distribution of the vegetation cover is relatively
high, lower temperatures lead to the formation of the
organic-mineral horizon called Mollic, which is characteristic of Rendolls.
• Mineral accumulation processes (Cumulization):
These processes include both the accumulation of soil
material by wind and water. In Libya, these processes are
mainly responsible for the formation of sand dunes and
Psamments (which is most widespread in the Libyan
soil). As well as the Fluvents which are formed along
flood plains by alluvial (water-deposited) soils. Also,
these processes lead to a delay in the development of the
soil profile, due to the lack of sufficient time for other soil
formation processes to involve in the development of the
soil profile.
3.4.1.2 The Processes of Loss Mineral
and Organic Materials from the Soil
Surface (Losses)
• Leaching (removal of soluble materials): Leaching is
the removal of soluble materials from one zone in soil to
another via water movement in the profile. These processes include washing the water-soluble salts (e.g., calcium and gypsum) inside the soil profile to a deep depth.
The occurrence of this process requires an adequate
amount of water. Therefore, the complete washing of
these materials from the soil profile is limited in areas that
receive high precipitation rates such as the northeastern
region of the country (i.e., Al Jabal Al Akhdar).
• Erosion (removal of the surface layer): The occurrence
of this process leads to the loss of the soil surface layer
through soil erosion by wind and/or water. These processes
are very active in Libyan soils and lead to a delay in the
development of soil profile. As a result, a (Truncated profile) is formed, and that is what usually happens in the soils
of Xeralfs in the Al Jabal Al Akhdar region.
3.4.1.3 Transfers of Organic and Mineral
Materials Within the Soil Profile
(Transformations)
These processes are similar to the previous processes, but the
materials are not completely lost from the soil profile, rather
they are transported from one place and deposited in another
place within the same soil profile. These processes also need
adequate water, but not the same amount of water needed for
the leaching processes. Such processes are responsible for
the formation of many subsurface diagnostic horizons, and
among these processes are the following:
• The process of transporting the water-soluble salts
from the surface by rainwater: Salts are deposited in
the subsurface layers forming the saline horizon (Salic),
in which the percentage of salts is more than 2% (i.e.,
Salids).
• The process of transporting the calcium carbonate
from the surface by rainwater: During this process,
calcium carbonate is deposited at varying depths
according to the amount of precipitation. This process is
responsible for the formation of the Calcic horizon, the
Petrocalcic horizon, and the Caliche layer, as in the case
of Calcid soils.
• The process of transporting the gypsum (dihydrate
calcium sulfate) from the surface by rainwater: In this
process, gypsum is deposited at different depths,
according to the precipitation rates in the area. This
process is responsible for the formation of the gypsum
horizons (Gypsic or Petrogypsic). These horizons may be
formed by transferring gypsum from the groundwater
level close to the surface, as in some Sabkhas. Usually,
gypsum in this case is below the saline horizon (Salic), as
in the case of the Gypsids.
• The process of transporting the Silicate clay (Illuviation): The process of transporting silicate clay minerals to
the subsurface layers is a water-assisted transport in a
basically vertical direction. First, the hydrolysis process
needs to take place to form secondary clay minerals in the
soil. Thus, this process requires a sufficient amount of
water (high humidity conditions). Therefore, this process
is very rare and occurs in Libyan soils. However, it was
found that the Libyan soils contain the clay horizon
(Argillic) and the Sodic horizon called Natric. Scientists
have indicated that the existence of the clay horizons in
arid soils can be explained by one of the following reasons (Dregne 2011; Ben Mahmoud 1995):
44
K. R. Ben Mahmoud and H. A. Zurqani