– Weathering of soil minerals and release of some
important elements such as potassium, phosphorous,
iron and, sulfur.
– The biological atmospheric nitrogen fixation.
– Mineralization (release of mineral constituents from
organic matter).
– Nitrification (the oxidation of the nitrite to nitrate).
– Denitrification (the reduction of nitrates or nitrites that
often results in the escape of nitrogen into the air).
– Process of reverse ionization occurs, i.e., converting
metallic nitrogen into a gaseous form.
– The oxidation of iron and other compounds.
All these processes and others may take place in the
Libyan soils once the conducive conditions are available.
3.4.2 Composite Processes of Soil Formation
Composite processes are a group of specific soil formation
processes that work together to form a particular type of soil,
under certain conditions of soil formation factors. This does
not mean that these soil formation processes work simultaneously together but may depend on each other. Usually,
each group of these processes is called by the name of the
soil formation process that produces it. There are many
processes that contribute to the formation of the Libyan
soils, the most important of which are the following (Ben
Mahmoud 1995):
• Salinization (accumulation of soluble salts): Insufficient
sedimentation for salt accumulation due to high temperatures and evaporation leads to the accumulation of salt in
the soil profile (Zurqani et al. 2019). The salinization
process redistributes the water-soluble salts within the
soil profile. This process takes place along the Libyan
coastal strip, in desperation areas with poor drainage, or
the dry marine pools in the contiguous areas of Benghazi.
Salinization may occur naturally or because of conditions
resulting from management practices. The soils formed
by this process are called Salids or Solonchack. These
soils are characterized by the fact that the percentage of
soluble salts may reach 2%, as well as the presence of the
saline horizon. These soils sometimes form what is
known as the white salt crust, and the process of redistribution of the water-soluble salts within the soil profile
in two ways is as following:
– Transfer of salts from the surface layers by the washing
processes and deposit in the subsurface layers.
– Transfer of salts from bottom to top when the
groundwater is close to the surface.
The preferred conditions to activate this process are a hot
and dry climate, low elevation, the close groundwater to the
surface, and the presence of the parent material that contains
high soluble salts.
• Salonization (sodicity): Sodicity refers to high sodium
(Na) levels in the soil. Soil sodicity is measured either
through its Exchangeable Sodium Percentage (ESP) or
Sodium Adsorption Ratio (SAR) (Zurqani et al. 2018).
During the Salonization process, the sodium element
replaces other chemical elements on the absorption complex of silicate clay minerals and humus. Also, a combination of sodium with carbonates occurs in the soil solution
to form sodium carbonate (Na 2 CO 3 ). Thus, the presence of
large amounts of sodium in the soils can cause soil dispersion, which prevents the formation of soil aggregates.
Sodium weakens the bonds between soil particles, which
leads to disperse and disburse of these particles. This process is responsible for the formation of the Natric horizon,
which is characterized by a prismatic or vertical structure
that limits the extension of roots in the soil. Consequently,
the sodic soils are formed (Natriargids or Solonetz).
The favored conditions for this process to occur are the
hot, dry climate, inability to completely wash out the salts
from the soil profile, and the presence of the parent material
with clayey texture. The predominant salt in this parent
material is sodium. This process takes place in limited and
very small areas in Libya (i.e., Al Jabal Al Akhdar region
and “Benghazi plain”), where the soils have a clayey texture.
Some of these soils can be managed by leaching out the
sodium present in the soil through the process called
Desolonization. It is the process that is used to reclaim the
sodic soils by adding agricultural gypsum (lime) to replace
sodium with calcium, with the addition of irrigation water to
wash salts from the soil profile.
• Calcification (Liming process): This is the general process by which calcium carbonate, and sometimes calcium
and magnesium carbonate, accumulates in the soils. Usually, the accumulation of calcium carbonate in subsoil
horizons is coupled with its removal from overlying horizons, linked by the downward translocation of the soluble
ions that precipitate to form calcium carbonate (CaCO 3 ).
This is according to the rates and conditions of washing.
This process is responsible for the formation of calcareous
soils, including the formation of the Calcic and Petrocalcic
horizons. In order for this process to occur, calcium carbonates (and sometimes calcium and magnesium carbonates) are transported or redistributed by rainwater or the
groundwater close to the surface (Dregne 2011).
46
K. R. Ben Mahmoud and H. A. Zurqani
important elements such as potassium, phosphorous,
iron and, sulfur.
– The biological atmospheric nitrogen fixation.
– Mineralization (release of mineral constituents from
organic matter).
– Nitrification (the oxidation of the nitrite to nitrate).
– Denitrification (the reduction of nitrates or nitrites that
often results in the escape of nitrogen into the air).
– Process of reverse ionization occurs, i.e., converting
metallic nitrogen into a gaseous form.
– The oxidation of iron and other compounds.
All these processes and others may take place in the
Libyan soils once the conducive conditions are available.
3.4.2 Composite Processes of Soil Formation
Composite processes are a group of specific soil formation
processes that work together to form a particular type of soil,
under certain conditions of soil formation factors. This does
not mean that these soil formation processes work simultaneously together but may depend on each other. Usually,
each group of these processes is called by the name of the
soil formation process that produces it. There are many
processes that contribute to the formation of the Libyan
soils, the most important of which are the following (Ben
Mahmoud 1995):
• Salinization (accumulation of soluble salts): Insufficient
sedimentation for salt accumulation due to high temperatures and evaporation leads to the accumulation of salt in
the soil profile (Zurqani et al. 2019). The salinization
process redistributes the water-soluble salts within the
soil profile. This process takes place along the Libyan
coastal strip, in desperation areas with poor drainage, or
the dry marine pools in the contiguous areas of Benghazi.
Salinization may occur naturally or because of conditions
resulting from management practices. The soils formed
by this process are called Salids or Solonchack. These
soils are characterized by the fact that the percentage of
soluble salts may reach 2%, as well as the presence of the
saline horizon. These soils sometimes form what is
known as the white salt crust, and the process of redistribution of the water-soluble salts within the soil profile
in two ways is as following:
– Transfer of salts from the surface layers by the washing
processes and deposit in the subsurface layers.
– Transfer of salts from bottom to top when the
groundwater is close to the surface.
The preferred conditions to activate this process are a hot
and dry climate, low elevation, the close groundwater to the
surface, and the presence of the parent material that contains
high soluble salts.
• Salonization (sodicity): Sodicity refers to high sodium
(Na) levels in the soil. Soil sodicity is measured either
through its Exchangeable Sodium Percentage (ESP) or
Sodium Adsorption Ratio (SAR) (Zurqani et al. 2018).
During the Salonization process, the sodium element
replaces other chemical elements on the absorption complex of silicate clay minerals and humus. Also, a combination of sodium with carbonates occurs in the soil solution
to form sodium carbonate (Na 2 CO 3 ). Thus, the presence of
large amounts of sodium in the soils can cause soil dispersion, which prevents the formation of soil aggregates.
Sodium weakens the bonds between soil particles, which
leads to disperse and disburse of these particles. This process is responsible for the formation of the Natric horizon,
which is characterized by a prismatic or vertical structure
that limits the extension of roots in the soil. Consequently,
the sodic soils are formed (Natriargids or Solonetz).
The favored conditions for this process to occur are the
hot, dry climate, inability to completely wash out the salts
from the soil profile, and the presence of the parent material
with clayey texture. The predominant salt in this parent
material is sodium. This process takes place in limited and
very small areas in Libya (i.e., Al Jabal Al Akhdar region
and “Benghazi plain”), where the soils have a clayey texture.
Some of these soils can be managed by leaching out the
sodium present in the soil through the process called
Desolonization. It is the process that is used to reclaim the
sodic soils by adding agricultural gypsum (lime) to replace
sodium with calcium, with the addition of irrigation water to
wash salts from the soil profile.
• Calcification (Liming process): This is the general process by which calcium carbonate, and sometimes calcium
and magnesium carbonate, accumulates in the soils. Usually, the accumulation of calcium carbonate in subsoil
horizons is coupled with its removal from overlying horizons, linked by the downward translocation of the soluble
ions that precipitate to form calcium carbonate (CaCO 3 ).
This is according to the rates and conditions of washing.
This process is responsible for the formation of calcareous
soils, including the formation of the Calcic and Petrocalcic
horizons. In order for this process to occur, calcium carbonates (and sometimes calcium and magnesium carbonates) are transported or redistributed by rainwater or the
groundwater close to the surface (Dregne 2011).
46
K. R. Ben Mahmoud and H. A. Zurqani