Agriculture Reference
In-Depth Information
on the need for adaptation, stating that even if emissions were to be stopped now,
greenhouse gases already in the atmosphere will continue to induce global warming.
Despite agriculture being a highly adaptive sector, there has been little effort geared
toward adapting crops and agricultural systems to upcoming changes in climate,
except for plant-breeding efforts to develop cultivars with increased resistance to
high temperatures and droughts.
m i t i g a t i of n of f C L i m a t e C h a n g e t h r o u g h s o i L C a r b o n
s e q u e s t r a t i of n a n D r e D u C t i o in s i n g r e e n h o u s e g a s e m i s s i of n s
Agricultural activities are very important from the point of view of climate change
because of their role in the emission and absorption of greenhouse gases. Agricultural
lands (cropland, grasslands, and permanent crops) occupy about 40% of the Earth's
land surface, estimated at 13.4 billion hectares. Historically, it is estimated that agri-
cultural soils have released to the atmosphere approximately 55 Pg (Petagram; one
billion metric tons) carbon (Cole et al., 1997) as a result of conversion of forests
and grasslands into croplands and application of management practices unable to
maintain adequate levels of soil organic matter (e.g., excessive tillage, insufficient
nutrient replacement). The agricultural sector is also the largest emitter of CH 4 , due
mainly to paddy rice cultivation and livestock activities (enteric fermentation), and
N 2 O, mainly due to excessive or untimely application of nitrogenous fertilizers.
Smith et al. (2008) estimated that agricultural activities currently emit about 6.1
Pg CO 2 -eq yr −1 (10 to 12% of total global anthropogenic emissions of greenhouse
gases). Methane emissions from agricultural activities represent about 3.3 Pg CO 2 -eq
yr −1 (50% of the world total), while N 2 O emissions represent 2.8 Pg CO 2 -eq yr −1 (60%
of world total). Carbon dioxide emissions are estimated to contribute about 0.04 Pg
CO 2 -eq yr −1 (~0% of world total).
Cole et al. (1997) estimated that agriculture could, during a period of 50 years,
contribute to the mitigation of CO 2 emissions by applying soil carbon sequestra-
tion practices aimed at the recovery of two thirds of the historical losses of soil
organic carbon. Figure 16.4 shows a simple representation of soil carbon sequestra-
tion in an agroecosystem. Organic carbon stabilizes in soil due to biochemical and
physicochemical mechanisms that operate at different spatial and temporal scales
(Jastrow et al., 2007). Soil carbon sequestration can be effected by such practices
as direct seeding (zero tillage, no till), efficient use of nutrients, crop intensification,
and residue management. For example, the adoption of direct-seeding systems in
several South American countries (Brazil, Argentina, Paraguay, and Uruguay) has
been very important recently. Izaurralde and Rice (2006) used global average soil
carbon sequestration rates of 0.57 Mg (Megagram; one metric ton) C ha −1 yr −1 (West
and Post, 2002) under no till and the global area under no till (~70 million hectares)
to estimate a soil carbon sink of about 40 Tg (Teragram; one million metric tons)
C yr −1 . Much work remains to be done to foster the adoption of this practice at global
scales and to design mechanisms to monitor soil carbon changes (Izaurralde and
Rice, 2006).
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