Agriculture Reference
In-Depth Information
Soil erosion, reduced fertility, or overgrazing
impacts up to ~40 % of global croplands
(Foley et al.
2005
).
The main driver of land-use change for agri-
culture was population growth. Now, in most
regions, it's shifting to dietary change (Kastner
et al.
2012
).
Cropland would have to be nearly doubled if
the projected global population of more than 9
billion people in 2050 were to have North
America's current diet and agricultural technol-
ogy. Cropland would have to be expanded 70 %
if the global population had Western Europe's
diet and technology (Kastner et al.
2012
).
satisfy additional production needs. Additional
greenhouse gas emissions due to increased
fertilizer use (primarily N
2
O) could be greater
than those arising from land-use change
(Mosnier et al.
2012
).
Using good cropland to expand (liquid) bio-
fuel production will likely exacerbate global
warming the same way as directly converting
forest and grasslands (Searchinger et al.
2008
). For example, increasing ethanol pro-
duction by 56 billion liters, which uses the
equivalent of 12.8 million hectares of maize in
the United States, would require bringing an
additional 10.8 million hectares of land into
cultivation to meet demand for maize for other
uses (Searchinger et al.
2008
).
The Organization for Economic Co-operation
and Development (OECD) and the United
Nations Food and Agriculture Organization
(FAO
2012
) project that from 2012 to 2021,
global ethanol and biodiesel production will
expand from 113 billion to 180 billion liters
annually. The largest markets - the United
States, Brazil, and the European Union - will
grow at a slower pace than in recent years
(USDA
2011
).
From 2012 to 2021, ethanol prices are
expected to increase from US$ 0.85 to 0.95
per liter, while biodiesel prices are expected to
increase from US$ 1.53 to 1.81 per liter.
Continued expansion is largely due to biofuel
policies, primary among them use mandates
and tax incentives (USDA
2011
), and high
crude oil prices.
3.2.8
Emissions from Production
of Biofuels
When compared to fossil fuels, manufactured liq-
uid biofuels do not necessarily produce fewer
greenhouse gas emissions.
The two key factors that determine whether
biofuels lead to lower or higher greenhouse
gas emissions than fossil fuels are:
- How the biomass (the basis of the biofuel)
is produced and harvested. This process
could emit carbon through, for example,
fertilizers and machinery.
- Where the biomass is produced. Biofuel
production that leads directly or indirectly
to land-use change emits high levels of
carbon.
The ethanol produced from a hectare of maize
reduces greenhouse gas emissions by 1.8 tons
of carbon dioxide equivalent (MtCO
2
e) per
hectare per year compared to the oil equiva-
lent. But each hectare of forest, grasslands, or
savannahs converted to cropland emits green-
house gases when the carbon-storing biomass
that makes up these biomes is cut down. For
forests, these “up-front” emissions are 604-
1,146 MtCO
2
e per hectare depending on forest
type and maturity; for grasslands or savan-
nahs, these emissions are 75-305 MtCO
2
e
(Searchinger et al.
2008
).
Some liquid biofuel policy alternatives could
signifi cantly increase global fertilizer use to
3.2.9
Biomass Burning
Burning of crop residues in fi elds is practiced for
clearing the land rapidly and inexpensively and
allowing the tillage practices to proceed unim-
peded by the residual crop material during prepa-
rations for the next growing season. The crops
whose residues are normally burnt in India and in
many other countries are rice, wheat, cotton,
maize, millet, sugarcane, jute, pulses, rapeseed-
mustard, and groundnut. On burning, the crop
residues are converted into gases such as carbon
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