Geoscience Reference
In-Depth Information
of irrigated area will boost yield and residue returns, thereby
increasing soil carbon and also suppressing N
2
O emissions by
improving aeration (Follett, 2001; Reay et al
.,
2003; Lal, 2004a;
Monteny et al
.,
2006). However, the energy used for water deliv-
ery or higher moisture and fertiliser N inputs may offset this
gain through CO
2
and N
2
O emissions, respectively (Schlesinger
1999; Liebig et al., 2005; Mosier et al
.,
2005).
Rice management:
CH
4
emission from cultivated wetland rice
soil can be reduced by growing low exuding cultivars, draining
once or several times during the growing season, using efficient
water management during off-season by keeping the soil dry
or avoiding waterlogging and incorporating properly composted
organic materials/residues (may be by producing biogas) during
the dry period (Wang and Shangguan, 1996; Yagi et al., 1997;
Wassmann et al., 2000; Aulakh et al., 2001; Cai et al., 2000,
2003; Xu et al., 2000, 2003; Kang et al., 2002; Yan et al., 2003;
Cai and Xu, 2004; Smith and Conen, 2004; Khalil and Shearer,
2006). Frequently, however, draining may be constrained by
water supply and may partly offset the reduced CH
4
emission
benefit by increasing N
2
O emissions (Akiyama et al., 2005).
These practices will also increase productivity by enhancing
soil organic carbon stocks (Pan et al., 2006).
Agro-forestry:
Planting trees and other perennial species in
an agro-forestry system also increases soil carbon sequestration
(Guo and Gifford, 2002; Paul et al., 2003; Oelbermann et al.,
2004; Mutuo et al., 2005), but the effects on N
2
O and CH
4
emis-
sions are not well known (Albrecht and Kandji, 2003).
Land cover (use) change:
Increasing the land cover or chang-
ing land use, similar to the native vegetation over the entire land
area ('set-asides') or in localised spots such as grassed water-
ways, field margins and shelterbelts effectively converts drained
croplands back to wetlands, reducing emissions and increasing
carbon storage (Follett, 2001; Ogle et al., 2003; Falloon et al.,
2004; Freibauer et al., 2004; Lal, 2004b; Paustian et al., 2004).
Converting drained croplands back to wetland, however, may
stimulate CH
4
emissions because waterlogging creates anaero-
bic conditions (Paustian et al., 2004).
Grazing land
management
and pasture
improvement
Globally, the area under grazing lands is more than croplands
and is usually managed less intensively (Anonymous, 2006c).
The practices that reduce emissions and enhance removals of
GHG are discussed below.
Grazing intensity:
Grazing intensity and timing influence
the removal, growth, carbon allocation and flora of grasslands,
affecting the amount of carbon accrual in soils (Conant et al.,
