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H. Elbasiouny and F. Elbehiry
interacting with the atmosphere, and most sensitive to land use and environmental
changes [47]. It is supposed that the changes in SOC related to land-use change occur
almost entirely in the surface soil (i.e. 30 cm) because deep SOC is inert on timescales
<100 years and is transported slowly downward relative to plant sources. Because of
these assumptions, most ecosystem biogeochemistry models and researches, which
estimate the response of vegetation and soil to climate change, land management,
and other factors, consider C dynamics in only the upper 20–30 cm of soil [48].
The soil C or N stocks are determined from two key variables: (i) concentration
and (ii) bulk density (BD), which are both prone to changes over time. To quantify
the sequestration rate in soils based on frequent sampling designs, it is essential to
assess both variables every time [49]. The BD is required for converting soil C or
N measurements (e.g., mg C g
−1 soil) to an area base using units of area or volume
(e.g., g C m
−2 soil) [50]. However, many studies in the past did not include BD
measurements. The BD is a function of parent material, soil genesis in addition to
soil aggregate formation and may change by tillage and compaction because of land
use changes, erosion, seasonal wet/dry cycles, and anthropogenic disruption [49].
Bulk density is a critical soil property that influences many other soil properties and
functions such as infiltration rates, aeration, root proliferation, and plant growth.
Since BD is one of a critical component of stocks measurement and it can be altered
by land use and land covers, careful and spatially-intensive measurements of BD are
critical for accurate extrapolations. Although BD is a simple soil attribute and widely
assessed by ecologists, engineers, and soil scientists, minor differences in methods
can cause considerable impact estimates of C or nutrient stocks sizes [50].
Bulk density is negatively correlated with SOC or soil N concentration in many
soils [49, 51, 52, 53]. The correlation between SOC and BD has been used widely
to estimate BD from SOC concentrations [49, 52, 53]. The SOC stocks may also be
underestimated because of increasing bulk density, as SOC stocks are a function of
bulk density and SOC concentration [41]. This also is applied on soil N stocks. However, stocks inventories cannot be completed using only one of these two variables,
even though both were weakly correlated with each other [49].
7 Factors Controlling of Carbon Stocks in the Soil
Many factors determine the maximum soil C stock and SOC sequestration such as the
age of ecosystem, climate, parent material, physiography, drainage, and soil properties (i.e. clay content, clay minerals, nutrient reserves …). As well, soil drainage and
moisture regime, beside soil aspect and landscape position [54], plant species composition, root biomass, period of the experiment are important factors controlling
soil C stock [22, 25, 26]. For example, total SOC can be increased with increasing
precipitation, while the opposite is true with increasing temperature. Under similar
climate conditions, soil texture may be the controlling factor of SOC outputs through
decomposition because there is a negative relationship between SOC mineralization
rate and soil clay + silt content [22]. Indeed, land-use has been realized as a key
H. Elbasiouny and F. Elbehiry
interacting with the atmosphere, and most sensitive to land use and environmental
changes [47]. It is supposed that the changes in SOC related to land-use change occur
almost entirely in the surface soil (i.e. 30 cm) because deep SOC is inert on timescales
<100 years and is transported slowly downward relative to plant sources. Because of
these assumptions, most ecosystem biogeochemistry models and researches, which
estimate the response of vegetation and soil to climate change, land management,
and other factors, consider C dynamics in only the upper 20–30 cm of soil [48].
The soil C or N stocks are determined from two key variables: (i) concentration
and (ii) bulk density (BD), which are both prone to changes over time. To quantify
the sequestration rate in soils based on frequent sampling designs, it is essential to
assess both variables every time [49]. The BD is required for converting soil C or
N measurements (e.g., mg C g
−1 soil) to an area base using units of area or volume
(e.g., g C m
−2 soil) [50]. However, many studies in the past did not include BD
measurements. The BD is a function of parent material, soil genesis in addition to
soil aggregate formation and may change by tillage and compaction because of land
use changes, erosion, seasonal wet/dry cycles, and anthropogenic disruption [49].
Bulk density is a critical soil property that influences many other soil properties and
functions such as infiltration rates, aeration, root proliferation, and plant growth.
Since BD is one of a critical component of stocks measurement and it can be altered
by land use and land covers, careful and spatially-intensive measurements of BD are
critical for accurate extrapolations. Although BD is a simple soil attribute and widely
assessed by ecologists, engineers, and soil scientists, minor differences in methods
can cause considerable impact estimates of C or nutrient stocks sizes [50].
Bulk density is negatively correlated with SOC or soil N concentration in many
soils [49, 51, 52, 53]. The correlation between SOC and BD has been used widely
to estimate BD from SOC concentrations [49, 52, 53]. The SOC stocks may also be
underestimated because of increasing bulk density, as SOC stocks are a function of
bulk density and SOC concentration [41]. This also is applied on soil N stocks. However, stocks inventories cannot be completed using only one of these two variables,
even though both were weakly correlated with each other [49].
7 Factors Controlling of Carbon Stocks in the Soil
Many factors determine the maximum soil C stock and SOC sequestration such as the
age of ecosystem, climate, parent material, physiography, drainage, and soil properties (i.e. clay content, clay minerals, nutrient reserves …). As well, soil drainage and
moisture regime, beside soil aspect and landscape position [54], plant species composition, root biomass, period of the experiment are important factors controlling
soil C stock [22, 25, 26]. For example, total SOC can be increased with increasing
precipitation, while the opposite is true with increasing temperature. Under similar
climate conditions, soil texture may be the controlling factor of SOC outputs through
decomposition because there is a negative relationship between SOC mineralization
rate and soil clay + silt content [22]. Indeed, land-use has been realized as a key