56
of crop residues, judicious use of nutrient amendments and organic substrates (e.g.
manuresand composts), minimal tillage, re-vegetation, and soil and water conservation measures (e.g., terracing, mulching, and contour plowing). For example, Raji
and Ogunwole (2006) observed sequestration at the rate of 0.24 Mg C ha
−1
year
−1
in
the 0–15 cm depth of soils after incorporation of crop residues in a study conducted
in Nigeria.
Finally, inclusion of green manure and leguminous cover crops (e.g., cow peas,
groundnuts, and velvet beans) in rotation cycle is also a promising SLM option for
soil C sequestration in SSA agricultural landscapes. Poeplau and Don (2015) conducted a meta-analysis to assess C sequestration in agricultural soils through cover
cropping and found that the time since introduction of cover crops in crop rotations
was linearly correlated with changes in SOC stocks with an annual change rate of
0.32 ± 0.08 Mg C ha
−1
year
−1
in a mean soil depth of 22 cm and during the observed
period of up to 54 years. Legume-based cropping systems reduce C and N losses
from the soil by improving soil aggregate stability and reducing erosion, improve
soil quality by increasing SOC through their biomass, and enhance the quality of
residue input and soil biodiversity (Lal 2004). Agro-ecosystems with high biodiversity are also known to absorb and sequester more C.
6 Concluding Remarks
To conclude, soils store substantial amounts of ecosystem C; hence, even slight
changes in SOC pool through land use changes can impact significantly on the C
cycle, climate, and soil quality. In SSA, the conversion of forests to cultivated lands
owing to population expansion has resulted in a reduction of the SOC stocks.
Restoring, conserving, and enhancing SOC stocks in SSA agro-ecosystems calls for
the adoption of a combination of appropriate SLM practices (e.g., CA), which can
capture and store C in plants and soils, as well as mitigate GHG emissions and climate change. SLM practices for soil C sequestration are well-documented and
ample information is available. This chapter has highlighted a number of such practices with potential to replenish SOC stocks in SSA; however, there is no one-sizefits-all or a magic bullet practice considering the diversity and heterogeneity of SSA
environments. Agricultural development and C sequestration projects in the region
should objectively select and scale out the best-fit SLM practices for specific contexts taking into account not only their potential for C sequestration (climate benefit) but also their technical feasibility, social acceptability, economic viability,
environmental benefits, and biodiversity benefits. Climate benefits of the selected
SLM technologies should be gauged both in terms of C sequestration rates and N 2 O
and CH 4 emissions associated with the technologies (i.e., abatement rates). The
agricultural development and C sequestration projects can also gain immensely
from policy frameworks, which foster multi-sectoral and multi-stakeholder partnerships, including the government, private sector, non-governmental organizations,
and farmers, for the effective, systematic, and coordinated scaling of SLM practices.
K. Were et al.
of crop residues, judicious use of nutrient amendments and organic substrates (e.g.
manuresand composts), minimal tillage, re-vegetation, and soil and water conservation measures (e.g., terracing, mulching, and contour plowing). For example, Raji
and Ogunwole (2006) observed sequestration at the rate of 0.24 Mg C ha
−1
year
−1
in
the 0–15 cm depth of soils after incorporation of crop residues in a study conducted
in Nigeria.
Finally, inclusion of green manure and leguminous cover crops (e.g., cow peas,
groundnuts, and velvet beans) in rotation cycle is also a promising SLM option for
soil C sequestration in SSA agricultural landscapes. Poeplau and Don (2015) conducted a meta-analysis to assess C sequestration in agricultural soils through cover
cropping and found that the time since introduction of cover crops in crop rotations
was linearly correlated with changes in SOC stocks with an annual change rate of
0.32 ± 0.08 Mg C ha
−1
year
−1
in a mean soil depth of 22 cm and during the observed
period of up to 54 years. Legume-based cropping systems reduce C and N losses
from the soil by improving soil aggregate stability and reducing erosion, improve
soil quality by increasing SOC through their biomass, and enhance the quality of
residue input and soil biodiversity (Lal 2004). Agro-ecosystems with high biodiversity are also known to absorb and sequester more C.
6 Concluding Remarks
To conclude, soils store substantial amounts of ecosystem C; hence, even slight
changes in SOC pool through land use changes can impact significantly on the C
cycle, climate, and soil quality. In SSA, the conversion of forests to cultivated lands
owing to population expansion has resulted in a reduction of the SOC stocks.
Restoring, conserving, and enhancing SOC stocks in SSA agro-ecosystems calls for
the adoption of a combination of appropriate SLM practices (e.g., CA), which can
capture and store C in plants and soils, as well as mitigate GHG emissions and climate change. SLM practices for soil C sequestration are well-documented and
ample information is available. This chapter has highlighted a number of such practices with potential to replenish SOC stocks in SSA; however, there is no one-sizefits-all or a magic bullet practice considering the diversity and heterogeneity of SSA
environments. Agricultural development and C sequestration projects in the region
should objectively select and scale out the best-fit SLM practices for specific contexts taking into account not only their potential for C sequestration (climate benefit) but also their technical feasibility, social acceptability, economic viability,
environmental benefits, and biodiversity benefits. Climate benefits of the selected
SLM technologies should be gauged both in terms of C sequestration rates and N 2 O
and CH 4 emissions associated with the technologies (i.e., abatement rates). The
agricultural development and C sequestration projects can also gain immensely
from policy frameworks, which foster multi-sectoral and multi-stakeholder partnerships, including the government, private sector, non-governmental organizations,
and farmers, for the effective, systematic, and coordinated scaling of SLM practices.
K. Were et al.