Geoscience Reference
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with 1405 Mha or 28% (Anonymous, 2006c). During the past
four decades, driven by increasing population pressure, agri-
cultural land increased by 500 Mha added from other land
uses, especially in the developing world with the conversion
of 6 Mha forests and 7 Mha other land annually, with a pro-
jection of an additional 500 Mha up to 2020 mostly in Latin
America and sub-Saharan Africa (Fedoroff and Cohen,
1999; Rosegrant et al., 2001; Huang et al., 2002; Trewavas,
2002; Green et al., 2005). Technological progress has enabled
remarkable improvements in land productivity and increasing
per capita food availability, although from a per capita declin-
ing land availability. The share of animal diets has consistently
increased, particularly poultry in the developing countries of
South and South-East Asia and sub-Saharan Africa due to eco-
nomic progress and changing lifestyles (Rosegrant et al., 2001;
Roy et al., 2002; Smith et al., 2007a). Annual GHG emissions
from agriculture are expected to rise in the coming decades
due to escalating demands of food and shifts in diet. The main
trend in the agricultural sector with the implications for GHG
emissions or removals can be outlined as follows:
•
Driven by the declining rate of land productivity, the use
of marginal lands (increase in the risk of soil erosion/
degradation), more irrigation, fertiliser and energy (for
moving and manufacturing fertiliser) will increase CO
2
emission (Schlesinger, 1999; Mosier, 2001; Lal 2004a,b;
Van Oost et al., 2004).
•
Globally, in 1999, the area under zero-tillage was 50 Mha,
which was 3.5% of the total arable land and is increas-
ingly adopted (Anonymous, 2001c). However, such prac-
tices are frequently combined with periodical tillage,
making the assessments of GHG balance highly uncertain
(Smith et al., 2007a). Furthermore, the use of agricultural
products such as bio-plastics, bio-fuels and biomass as
substitutes for fossil fuel-based products is an encourag-
ing trend that has a potential to reduce GHG emissions.
•
Growing demand of animal products may further accel-
erate land use change (from forest to grassland) and
larger herds of livestock with higher manure produc-
tion and management thus will increase GHG emission
(Smith et al., 2007a).
•
In a more open-market economy-driven world with
changes in policies (e.g. subsidies), encouraging interna-
tional trade of agricultural products caused by regional
