55
can boost the amount of organic materials returned to the soil, especially in the
ASALs, and build up SOC pools both in the short and long term. For instance, a
study by Gebeyehu and Soromessa (2018) in northwest Ethiopia showed that the
mean SOC stock was higher by 2.85 Mg C ha
−1
(3.44%) in the surface soils (0–30 cm
depth) of irrigated compared to rain-fed farming systems. The irrigated farming
system sequestered C at the rate of 0.41 Mg C ha
−1
year
−1
.
Grazing and pasture management is another SLM practice that can contribute
significantly to soil C sequestration in the SSA agricultural systems. By introducing
improved grass species with higher productivity and C allocation to deeper roots;
reducing the frequency and extent of fires through effective fire suppression means;
burning at a time of the year when less amounts of CO 2 , CH 4 , and N 2 O are emitted;
reducing the fuel load through appropriate vegetation management; restoring the
degraded grazing lands (through exclosures); improving soil fauna (e.g., earthworms and termites), irrigation, fertilization, and legume integration; managing the
stocking rates; and adjusting the timing of grazing, optimal soil C sequestration and
re-carbonization can be realized (UNFCCC 2008; Smith et al. 2007). The World
Bank (2012) indicated that attainable rate of soil C sequestration through improved
management was about 0.8 Mg C ha
−1
year
−1
on average in Africa. Conant et al.
(2017) also synthesized data from various studies and confirmed that C sequestration rates were positive for most improved grazing and pasture management practices, with an average of 0.47 Mg C ha
−1
year
−1
across all studies. Derner and
Schuman (2007), Rimhanen et al. (2016), and Gebregergs et al. (2019) are among
the other authors who have reported similar results.
Furthermore, restorative land uses that favor conservation and improvement of
soil, water, and air quality have potential for soil C sequestration in SSA agroecosystems. For instance, introducing agro-forestry and reverting marginal croplands to native systems can culminate in an accrual of SOC owing to higher
aboveground biomass C, reduced soil disturbance, and minimal removal of residue
and harvested products. The C sequestration rates in agro-forestry soils can significantly differ among agro-forestry systems (e.g., type, age, tree species, and management), climates, and soils (e.g., type, depth, and severity of degradation). Vågen
et al. (2005) reported high potentials for C sequestration after establishment of
improved (tree) fallow systems with the attainable rates ranging from 0.07 to
1.37 Mg C ha
−1
year
−1
. Lorenz and Lal (2014) also established that about 0.06 Mg
C ha
−1
year
−1
was sequestered in the topsoil (0–15 cm) of a 25-year-old agro- forestry
system consisting of cacao (Theobroma cacao) and salmwood (Cordia alliodora) in
Ghana. Moreover, Luedeling et al. (2011) noted that agro-forestry systems, such as
parklands, live fences, and home gardens, in Africa accumulated C at the rate of
0.2–0.8 Mg C ha
−1
year
−1
, while rotational woodlots sequestered at the rate of
2.2–5.8 Mg C ha
−1
year
−1
. Apart from agro-forestry, restoration of drained wetlands
(or peat lands) and degraded soils can also enhance soil C sequestration and mitigate CO 2 emissions. Wetlands are characterized by peaty soils, which accumulate C
because of the slow rate of decomposition under anaerobic conditions even though
such conditions can also instigate CH 4 emissions if not properly managed. For the
degraded soils, re-carbonization can be achieved through practices such as retention
Land Use Changes and Sustainable Land Management Practices for Soil Carbon…
can boost the amount of organic materials returned to the soil, especially in the
ASALs, and build up SOC pools both in the short and long term. For instance, a
study by Gebeyehu and Soromessa (2018) in northwest Ethiopia showed that the
mean SOC stock was higher by 2.85 Mg C ha
−1
(3.44%) in the surface soils (0–30 cm
depth) of irrigated compared to rain-fed farming systems. The irrigated farming
system sequestered C at the rate of 0.41 Mg C ha
−1
year
−1
.
Grazing and pasture management is another SLM practice that can contribute
significantly to soil C sequestration in the SSA agricultural systems. By introducing
improved grass species with higher productivity and C allocation to deeper roots;
reducing the frequency and extent of fires through effective fire suppression means;
burning at a time of the year when less amounts of CO 2 , CH 4 , and N 2 O are emitted;
reducing the fuel load through appropriate vegetation management; restoring the
degraded grazing lands (through exclosures); improving soil fauna (e.g., earthworms and termites), irrigation, fertilization, and legume integration; managing the
stocking rates; and adjusting the timing of grazing, optimal soil C sequestration and
re-carbonization can be realized (UNFCCC 2008; Smith et al. 2007). The World
Bank (2012) indicated that attainable rate of soil C sequestration through improved
management was about 0.8 Mg C ha
−1
year
−1
on average in Africa. Conant et al.
(2017) also synthesized data from various studies and confirmed that C sequestration rates were positive for most improved grazing and pasture management practices, with an average of 0.47 Mg C ha
−1
year
−1
across all studies. Derner and
Schuman (2007), Rimhanen et al. (2016), and Gebregergs et al. (2019) are among
the other authors who have reported similar results.
Furthermore, restorative land uses that favor conservation and improvement of
soil, water, and air quality have potential for soil C sequestration in SSA agroecosystems. For instance, introducing agro-forestry and reverting marginal croplands to native systems can culminate in an accrual of SOC owing to higher
aboveground biomass C, reduced soil disturbance, and minimal removal of residue
and harvested products. The C sequestration rates in agro-forestry soils can significantly differ among agro-forestry systems (e.g., type, age, tree species, and management), climates, and soils (e.g., type, depth, and severity of degradation). Vågen
et al. (2005) reported high potentials for C sequestration after establishment of
improved (tree) fallow systems with the attainable rates ranging from 0.07 to
1.37 Mg C ha
−1
year
−1
. Lorenz and Lal (2014) also established that about 0.06 Mg
C ha
−1
year
−1
was sequestered in the topsoil (0–15 cm) of a 25-year-old agro- forestry
system consisting of cacao (Theobroma cacao) and salmwood (Cordia alliodora) in
Ghana. Moreover, Luedeling et al. (2011) noted that agro-forestry systems, such as
parklands, live fences, and home gardens, in Africa accumulated C at the rate of
0.2–0.8 Mg C ha
−1
year
−1
, while rotational woodlots sequestered at the rate of
2.2–5.8 Mg C ha
−1
year
−1
. Apart from agro-forestry, restoration of drained wetlands
(or peat lands) and degraded soils can also enhance soil C sequestration and mitigate CO 2 emissions. Wetlands are characterized by peaty soils, which accumulate C
because of the slow rate of decomposition under anaerobic conditions even though
such conditions can also instigate CH 4 emissions if not properly managed. For the
degraded soils, re-carbonization can be achieved through practices such as retention
Land Use Changes and Sustainable Land Management Practices for Soil Carbon…