Agriculture Reference
In-Depth Information
are responsible for about 75% of agricultural
GHG emissions, also represent the largest share,
about 70%, of the total mitigation potential
(IPCC, 2007; UNFCCC, 2008).
Thus, managing soil C has implications
both in terms of sources and sink of atmos-
pheric CO 2 . But the AFOLU sector must,
above all, face the important challenge of
supporting food production and food secur-
ity. This imperative is recognized in the
UNFCCC, where it is stated that stabiliza-
tion of GHGs must be achieved while ensur-
ing that food production is not threatened.
Thus, particularly following the food crises
of 2008 and 2009, the international debate
has shifted somewhat away from GHG miti-
gation in the AFOLU sector towards food
security and sustainability goals in other
international agreements and initiatives
(e.g. United Nations Convention to Combat
Desertification (UNCCD), Convention on
Biological Diversity (CBD), Global Soil Part-
nership, Rio+20, etc.), with a greater focus
on adapting to climate changes and extreme
climate events. However, adopting practices
to achieve GHG mitigation and improving
food security and soil sustainability are not,
in most cases, mutually exclusive. Indeed,
they can often be complementary in that
SCS allows for the replenishment of soil or-
ganic matter, thereby providing several other
benefits, including improved soil structure
and stability that leads to reduced soil ero-
sion, improved soil biodiversity, increased
nutrient-holding capacity, increased nutri-
ent-use efficiency, increased water-holding
capacity and increased crop yields. More-
over, carbon in soil improves the resilience
of cropping systems against both excess and
lack of water, and accompanying improve-
ments in soil biodiversity increases resilience
to changing environmental conditions and
stresses. Therefore, it strengthens the capacity
to face extreme events (climate adaptation).
Most mitigation and adaptation solutions
are interrelated, and both must be planned
together. In arid and semi-arid regions, soil
degradation is widespread and most dry-
land soils are already degraded or are at high
risk of degradation. Due to natural constraints,
dryland soils contain a very small amount of
carbon (typically below 1%). Thus, maintaining
a minimum soil organic matter level is crit-
ical to maintain soil function. It is evident
that in arid and semi-arid regions, SCS is
more important for the non-GHG benefits, in
terms of economic and social impacts, than
the absolute amount of carbon sequestered.
The objectives of this chapter are thus
to provide an updated overview of the dif-
ferent approaches for encouraging SCS, but
also to give a focus on common erroneous
shortcuts still present in the debate of miti-
gation and agriculture. Finally, this chapter
will also discuss and propose solutions for
removing barriers to the full implementa-
tion of SCS solutions into policies.
Options and Practices to Mitigate
through Soil Carbon Sequestration
atĀ Field Scale
Many mitigation options focus on increas-
ing SOC in the soil profile, but managing
soils also influences fluxes of CH 4 and N 2 O.
Thus, to account for the overall GHG balance,
Bernoux et al . (2006) proposed a definition
of SCS: 'SCS for a specific agroecosystem, in
comparison with a reference, should be
considered as the result for a given period of
time and portion of space of the net balance
of all GHG expressed in C-CO 2 -equivalent
or CO 2 -equivalent, computing all fluxes at
the soil-plant-atmosphere interface, but also
the indirect fluxes (gasoline, enteric fermen-
tation, etc).' A number of detailed reviews
of agricultural management practices being
promoted for SCS and GHG reductions have
been published recently (e.g. Ogle et al .,
2005; Smith et al ., 2007; Eagle et al ., 2010;
Denef et al ., 2011). Here, we present a brief
overview of different types of activities
from a global perspective.
The IPCC (2007) published global esti-
mates of SCS (net change considering all
direct GHGs, expressed as CO 2 -eq) of broad
sustainable land management categories,
namely agronomy, nutrient management,
tillage/residue management, water manage-
ment and agroforestry ( Table 9.1 ). Briefly, the
'agronomy' category corresponds to practices
that may increase yields and thus generate
 
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