In sodic soils, sodium ions are attached to clay particles.
The monovalency of sodium cations leads to a loss in the
stickiness of clay particles when wet. If the proportion of
divalent ions is reduced, the aggregate formation will also be
reduced. This leads to collapsed and unstable soils that
become impermeable to water and roots and which erode
easily (Tanji 1996; ILACO 1989; Landon 1984). The FAO
(1988) conclude that plant growth is adversely affected in
sodic soils due to one or more of the following factors:
firstly, high ESP in sodic soils markedly influences the
physical soil properties. Secondly, the effect of ESP on plant
growth is through its effect on soil pH. A high pH could
affect greatly lowering the availability of essential plant
nutrients such as Calcium, Magnesium, phosphorus, iron,
manganese, and zinc.
Yeha (1982) classified the plants in Libya into five categories according to ESP tolerance. The classification was
based on the USDA classification. Ben Mahmoud (1995)
points out that ESP in some Entisols in the south of Libya
has been found to be between 3 and 28%. Ben Mahmoud
believes that the main reason for this high ESP is not the
high sodium but the low CEC in these sandy soils. He argues
that the CEC is very low and ranges from 1 to 10 me/100 g
soil. Therefore, crops in such soils may not be affected by
the sodium even though the ESP appears to be high. This
could be true in the south of the country and some parts of
the North West; however, in the North East of Libya, the
CEC is relatively higher (Zurqani et al. 2018).
In general, soil sodicity is believed to be one of the
limiting factors facing agriculture development in Libya.
The effect of soil sodicity is apparent in Libya, especially in
the North East of the country where the good soils exist with
high clay content and relatively high soil cation exchange
capacity (CEC).
5.2.6 Calcium Carbonate Content
Carbonates in soil profiles may be derived from
carbonate-rich rocks but it can be encountered as secondary
depositions from groundwater (Landon 1984). Calcium
carbonate (CaCO 3 ) in the form of free lime in the soil profile
affects soil structure and interferes with infiltration and the
evapotranspiration process. It influences both the soil
moisture regime and the availability of nutrients (FAO
2002). The higher percentage of calcium carbonate in the
soil, the worse its various properties, and consequently the
lower its productivity and the fewer the chances of cultivating crops in it. The presence of calcium carbonate in high
content leads to weak soil structure and thus increases the
degree of water loss throughout the soil profile. The high
percentage of calcium carbonate leads to a decrease in the
CEC and a rise in the pH. And the last one leads to the
conversion of some nutrient elements such as phosphorous,
iron, and zinc into a form that is not available for absorption
by plants.
Calcium carbonate being only slowly soluble does not
affect plants at the percentage levels at which soluble salts
become harmful but may have adverse effects when present
in high concentrations, including as calcic horizons. This is
most likely to occur in semiarid regions (ILACO 1989).
Calcium carbonate can form hardpans, including Petrocalcic
horizon, in which calcium carbonate cement the soil particles. The net effect of these dense horizons is to delay or
prevent root growth and thus limit the effective depth of the
soil. They also may affect soil oxygenation by restricting
drainage at times in which large amounts of water are present. Therefore, calcium carbonate represents one of the
limiting factors of agricultural production. In Libya, the dry
climatic conditions help to have a high accumulation of
calcium carbonate in the soils. Calcids, Petrocalcids, and
Rendolls are the major soils that have a high percentage of
CaCO 3 (Ben Mahmoud 1995).
5.2.7 Nutrients
Libyan soils are characterized by their low content of
nitrogen, available phosphorous, and available trace elements, especially zinc and iron. Nitrogen is bound in the soil
with organic matter, which is considered low to very low in
Libyan soils. As for the lack of available phosphorus in the
Libyan soils, it is mainly due to the increase in soil pH and
the content of calcium carbonate, which turns it into a form
that is not available for absorption by plants. Also, the high
soil pH level decreases the availability of zinc, iron, and in
some cases manganese and copper. Therefore, if these
nutrients are not added during the cultivation of agricultural
crops in Libyan soils in the appropriate quantity and manner,
then these elements are considered a factor limiting the
growth of most agricultural crops and reducing the productivity of some others (Ben Mahmoud 1995).
5.3 Other Constraints to Agricultural Use
and Development
There are many other constraints to agriculture use and
development in Libya other than the soil factors such as
climate, water resources, terrain, and soil erosion. These
factors can be also considered as the main limiting factors in
agriculture productivity. The following is a brief description
of these factors and their influences on agricultural expansion and increasing agricultural productivity.
5 Major Limiting Factors Affecting Agricultural Use and Production
69
The monovalency of sodium cations leads to a loss in the
stickiness of clay particles when wet. If the proportion of
divalent ions is reduced, the aggregate formation will also be
reduced. This leads to collapsed and unstable soils that
become impermeable to water and roots and which erode
easily (Tanji 1996; ILACO 1989; Landon 1984). The FAO
(1988) conclude that plant growth is adversely affected in
sodic soils due to one or more of the following factors:
firstly, high ESP in sodic soils markedly influences the
physical soil properties. Secondly, the effect of ESP on plant
growth is through its effect on soil pH. A high pH could
affect greatly lowering the availability of essential plant
nutrients such as Calcium, Magnesium, phosphorus, iron,
manganese, and zinc.
Yeha (1982) classified the plants in Libya into five categories according to ESP tolerance. The classification was
based on the USDA classification. Ben Mahmoud (1995)
points out that ESP in some Entisols in the south of Libya
has been found to be between 3 and 28%. Ben Mahmoud
believes that the main reason for this high ESP is not the
high sodium but the low CEC in these sandy soils. He argues
that the CEC is very low and ranges from 1 to 10 me/100 g
soil. Therefore, crops in such soils may not be affected by
the sodium even though the ESP appears to be high. This
could be true in the south of the country and some parts of
the North West; however, in the North East of Libya, the
CEC is relatively higher (Zurqani et al. 2018).
In general, soil sodicity is believed to be one of the
limiting factors facing agriculture development in Libya.
The effect of soil sodicity is apparent in Libya, especially in
the North East of the country where the good soils exist with
high clay content and relatively high soil cation exchange
capacity (CEC).
5.2.6 Calcium Carbonate Content
Carbonates in soil profiles may be derived from
carbonate-rich rocks but it can be encountered as secondary
depositions from groundwater (Landon 1984). Calcium
carbonate (CaCO 3 ) in the form of free lime in the soil profile
affects soil structure and interferes with infiltration and the
evapotranspiration process. It influences both the soil
moisture regime and the availability of nutrients (FAO
2002). The higher percentage of calcium carbonate in the
soil, the worse its various properties, and consequently the
lower its productivity and the fewer the chances of cultivating crops in it. The presence of calcium carbonate in high
content leads to weak soil structure and thus increases the
degree of water loss throughout the soil profile. The high
percentage of calcium carbonate leads to a decrease in the
CEC and a rise in the pH. And the last one leads to the
conversion of some nutrient elements such as phosphorous,
iron, and zinc into a form that is not available for absorption
by plants.
Calcium carbonate being only slowly soluble does not
affect plants at the percentage levels at which soluble salts
become harmful but may have adverse effects when present
in high concentrations, including as calcic horizons. This is
most likely to occur in semiarid regions (ILACO 1989).
Calcium carbonate can form hardpans, including Petrocalcic
horizon, in which calcium carbonate cement the soil particles. The net effect of these dense horizons is to delay or
prevent root growth and thus limit the effective depth of the
soil. They also may affect soil oxygenation by restricting
drainage at times in which large amounts of water are present. Therefore, calcium carbonate represents one of the
limiting factors of agricultural production. In Libya, the dry
climatic conditions help to have a high accumulation of
calcium carbonate in the soils. Calcids, Petrocalcids, and
Rendolls are the major soils that have a high percentage of
CaCO 3 (Ben Mahmoud 1995).
5.2.7 Nutrients
Libyan soils are characterized by their low content of
nitrogen, available phosphorous, and available trace elements, especially zinc and iron. Nitrogen is bound in the soil
with organic matter, which is considered low to very low in
Libyan soils. As for the lack of available phosphorus in the
Libyan soils, it is mainly due to the increase in soil pH and
the content of calcium carbonate, which turns it into a form
that is not available for absorption by plants. Also, the high
soil pH level decreases the availability of zinc, iron, and in
some cases manganese and copper. Therefore, if these
nutrients are not added during the cultivation of agricultural
crops in Libyan soils in the appropriate quantity and manner,
then these elements are considered a factor limiting the
growth of most agricultural crops and reducing the productivity of some others (Ben Mahmoud 1995).
5.3 Other Constraints to Agricultural Use
and Development
There are many other constraints to agriculture use and
development in Libya other than the soil factors such as
climate, water resources, terrain, and soil erosion. These
factors can be also considered as the main limiting factors in
agriculture productivity. The following is a brief description
of these factors and their influences on agricultural expansion and increasing agricultural productivity.
5 Major Limiting Factors Affecting Agricultural Use and Production
69