Soil Carbon Sequestration for Climate Change Mitigation …
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Nitrogen is frequently a limiting factor for growth and re-establishment of vegetation in disturbed or degraded soils. Thus it is essential for increasing SOC concentrations. Therefore, inputs of N should be considered in any future restoration and
sequestration efforts. Total N (TN) and SOC are largely related to SOM accumulation, and hence, always follow similar patterns [41]. Because of this joined cycling of
C and N, assessment of the total nitrogen (TN) is important in all SOC stock studies
because of the effective impact of soil N dynamic on SOC sequestration [42, 43].
There is a rising research interest in N deposition effects on carbon sequestration
in forest ecosystems. Increased N deposition can affect forest ecosystems in several
directions such as increment of foliar biomass and efficiency of photosynthesis, and
thus increase forest ecosystem biomass, reducing allocation to fine roots, reducing
respiration rates, accelerating N saturation in areas of high nitrogen in soils, and
consequently cause leaching loss of N and base cations to aquatic systems. It was
suggested that N deposition may increase the net primary production (NPP) at first,
but then NPP declines with N saturation which will affect acquiring atmospheric
therefore an affecting sequestered C. However, there is a suggestion to consider
regional or site-specific in the investigation the effects of increasing N input on C
sequestration [43]. It is stated that optimizing fertilizer N inputs, may increase SOC
content through increasing crop productivity and subsequently the residues amount
returned to soils. They also added that excessive N fertilization might suppress the
microbial communities or stimulation of mineralization of old native organic which
lead to blocking SOC sequestration [5]. In this context also, it is reported that the
amount of N sequestered or lost was still closely associated with the C dynamics,
showing that similar controls apply to both [44]. It is explained that the relationship
between C and N sequestration by that SOM, as indicated by soil C and N levels, can
directly impact crop production. The increase in crop production with increased SOM
storage is a result of enhancing soil structure and improving soil water–nutrient–
crop productivity relationships. Sequestration of C in the soil can also conserve N,
because SOC and total N (TN) levels are highly related [45]. Crop residues type,
and its properties (i.e. C/N ratios or quality of the residues) has an important role
in C sequestration and soil aggregation. C/N ratios often govern the degradation
of fresh crop residues, however, undergoing residues decomposition will make it
more recalcitrant. Subsequently, degradation becomes controlled by lignin contents
or lignin/N ratios. Thus, confirm on the ability of soils to sequester C is highly related
to N [46].
6 Required Variables for Calculating Soil C and N Stocks
The most appropriate method to study the organic C and N content in the soil is
on a unit area basis, for a specific interval depth. This requires more information
about the spatial variability of different soils and their content of C and N and bulk
density. Commonly, reference depth intervals of 0–0.3 m and 0–1 m are used in
studies of SOC stocks. The first layer encompasses the depths that are most directly
159
Nitrogen is frequently a limiting factor for growth and re-establishment of vegetation in disturbed or degraded soils. Thus it is essential for increasing SOC concentrations. Therefore, inputs of N should be considered in any future restoration and
sequestration efforts. Total N (TN) and SOC are largely related to SOM accumulation, and hence, always follow similar patterns [41]. Because of this joined cycling of
C and N, assessment of the total nitrogen (TN) is important in all SOC stock studies
because of the effective impact of soil N dynamic on SOC sequestration [42, 43].
There is a rising research interest in N deposition effects on carbon sequestration
in forest ecosystems. Increased N deposition can affect forest ecosystems in several
directions such as increment of foliar biomass and efficiency of photosynthesis, and
thus increase forest ecosystem biomass, reducing allocation to fine roots, reducing
respiration rates, accelerating N saturation in areas of high nitrogen in soils, and
consequently cause leaching loss of N and base cations to aquatic systems. It was
suggested that N deposition may increase the net primary production (NPP) at first,
but then NPP declines with N saturation which will affect acquiring atmospheric
therefore an affecting sequestered C. However, there is a suggestion to consider
regional or site-specific in the investigation the effects of increasing N input on C
sequestration [43]. It is stated that optimizing fertilizer N inputs, may increase SOC
content through increasing crop productivity and subsequently the residues amount
returned to soils. They also added that excessive N fertilization might suppress the
microbial communities or stimulation of mineralization of old native organic which
lead to blocking SOC sequestration [5]. In this context also, it is reported that the
amount of N sequestered or lost was still closely associated with the C dynamics,
showing that similar controls apply to both [44]. It is explained that the relationship
between C and N sequestration by that SOM, as indicated by soil C and N levels, can
directly impact crop production. The increase in crop production with increased SOM
storage is a result of enhancing soil structure and improving soil water–nutrient–
crop productivity relationships. Sequestration of C in the soil can also conserve N,
because SOC and total N (TN) levels are highly related [45]. Crop residues type,
and its properties (i.e. C/N ratios or quality of the residues) has an important role
in C sequestration and soil aggregation. C/N ratios often govern the degradation
of fresh crop residues, however, undergoing residues decomposition will make it
more recalcitrant. Subsequently, degradation becomes controlled by lignin contents
or lignin/N ratios. Thus, confirm on the ability of soils to sequester C is highly related
to N [46].
6 Required Variables for Calculating Soil C and N Stocks
The most appropriate method to study the organic C and N content in the soil is
on a unit area basis, for a specific interval depth. This requires more information
about the spatial variability of different soils and their content of C and N and bulk
density. Commonly, reference depth intervals of 0–0.3 m and 0–1 m are used in
studies of SOC stocks. The first layer encompasses the depths that are most directly