162
H. Elbasiouny and F. Elbehiry
different sizes. The protection of SOM is desirable in the soil since SOM is widely
recognized as a key component in nutrient cycling. Furthermore, the retention of SOC
is becoming more important since the rise in atmospheric CO 2 and global warming
are recent concerns [61].
7.2 Climate Conditions
Climatic shifts in temperature and precipitation significantly affect SOC because the
soil C sequestration is a function of both primary production and decomposition of
OM in agricultural soils [29]. Generally, SOC tends to accumulate in areas with lower
temperatures and higher precipitation [28]. Both the increase in global temperature
and the decrease of precipitation due to climate change may result in an overall
decrease in the SOC storage especially in the critical areas which have typically low
SOC contents such as Mediterranean areas. The agricultural soil in these areas are
particularly vulnerable to climate change, i.e. most climate models predict higherthan-average increases in temperature and generalized decreases in precipitations in
most of these areas [32].
7.3 Land Use
Land use is a key determining factor of soil carbon stocks. Any change in land use
influences on the flow of soil C stock to the new equilibrium point is finally reached
under the new land use conditions. The equilibrium C content is a key feature of
each soil depending on climate, soil type, vegetation nature and the balance between
C inflows and outflows under certain vegetation [62]. Land use change is the second
main reason for carbon emissions after fuel consumption [11]. Conversion from the
forest or natural grasslands for example to croplands can disturb soil and vegetation
and ultimately lead to a dramatic depletion of soil carbon stocks and nutrients [11, 16,
32, 62]. As well, land use affects SOC stocks mainly by changing plant species and
management practices [30]. Land use contributes approximately 25% of total global
anthropogenic GHG emissions, 10–14% of this total are resulted from agricultural
production either via emissions from soils or livestock management, while 12–17%
are from land cover change. Land use changes mainly have an influence of food,
fiber and fuel demands of a growing population can critically affect soil’s capacity to
store C [32]. Soils have lost 40–90 Pg C due to historical land-use, mainly through
deforestation and reclamation [30]. Mathew et al. [62] estimated that soils over the
world had lost between 25 and 75% of their C stocks due to some factors such as
soil degradation, vegetation changes and tillage operations. Land use change and
land mismanagement (such as the use of excessive plowing, residue removal and
biomass burning, and farming practices where nutrient balance is often negative)
have not only depleted SOC stocks dramatically but also leads to loss of C from
H. Elbasiouny and F. Elbehiry
different sizes. The protection of SOM is desirable in the soil since SOM is widely
recognized as a key component in nutrient cycling. Furthermore, the retention of SOC
is becoming more important since the rise in atmospheric CO 2 and global warming
are recent concerns [61].
7.2 Climate Conditions
Climatic shifts in temperature and precipitation significantly affect SOC because the
soil C sequestration is a function of both primary production and decomposition of
OM in agricultural soils [29]. Generally, SOC tends to accumulate in areas with lower
temperatures and higher precipitation [28]. Both the increase in global temperature
and the decrease of precipitation due to climate change may result in an overall
decrease in the SOC storage especially in the critical areas which have typically low
SOC contents such as Mediterranean areas. The agricultural soil in these areas are
particularly vulnerable to climate change, i.e. most climate models predict higherthan-average increases in temperature and generalized decreases in precipitations in
most of these areas [32].
7.3 Land Use
Land use is a key determining factor of soil carbon stocks. Any change in land use
influences on the flow of soil C stock to the new equilibrium point is finally reached
under the new land use conditions. The equilibrium C content is a key feature of
each soil depending on climate, soil type, vegetation nature and the balance between
C inflows and outflows under certain vegetation [62]. Land use change is the second
main reason for carbon emissions after fuel consumption [11]. Conversion from the
forest or natural grasslands for example to croplands can disturb soil and vegetation
and ultimately lead to a dramatic depletion of soil carbon stocks and nutrients [11, 16,
32, 62]. As well, land use affects SOC stocks mainly by changing plant species and
management practices [30]. Land use contributes approximately 25% of total global
anthropogenic GHG emissions, 10–14% of this total are resulted from agricultural
production either via emissions from soils or livestock management, while 12–17%
are from land cover change. Land use changes mainly have an influence of food,
fiber and fuel demands of a growing population can critically affect soil’s capacity to
store C [32]. Soils have lost 40–90 Pg C due to historical land-use, mainly through
deforestation and reclamation [30]. Mathew et al. [62] estimated that soils over the
world had lost between 25 and 75% of their C stocks due to some factors such as
soil degradation, vegetation changes and tillage operations. Land use change and
land mismanagement (such as the use of excessive plowing, residue removal and
biomass burning, and farming practices where nutrient balance is often negative)
have not only depleted SOC stocks dramatically but also leads to loss of C from