Geoscience Reference
In-Depth Information
practices that deliver added N more efficiently to crops often
reduce N
2
O emissions (Bouwman, 2001), and managing
livestock to make most efficient use of feeds often reduces
amounts of CH
4
produced (Clemens and Ahlgrimm, 2001). The
approaches that best reduce emissions depend on local condi-
tions and, therefore, vary from region to region.
enhanc ing
removals
Agricultural ecosystems stock large carbon reserves mostly in
the form of soil organic matter (Anonymous 2001a) which are
lost more than 50 Pg C (Paustian et al., 1998; Lal, 1999, 2001a,b;
2002, 2003, 2004a-e, 2005; Lal and Bruce, 1999; Lal et al.,
2003). This loss can be recovered through improved manage-
ment, thereby withdrawing atmospheric CO
2
. These practices
can be adopted locally to increase the photosynthetic input of
carbon and/or slow the return of stored carbon to CO
2
through
respiration, fire or erosion. This will increase carbon reserves
by sequestering carbon or stocking carbon sinks (Lal, 2004a)
through agro-forestry or other perennial plantings on agricul-
tural lands (Albrecht and Kandji, 2003). Agricultural and forest
lands also remove CH
4
from the atmosphere by oxidation, but
this effect is small compared to other GHG fluxes (Smith and
Conen, 2004; Tate et al., 2006).
Avoiding/
displacing
emissions
The combustion of bioenergy feedstock used as a source of
fuel either directly or after conversion releases CO
2
(Schneider
and McCarl, 2003; Cannell, 2003). The net benefit of bioen-
ergy sources to the atmosphere is equal to the fossil-derived
emissions displaced, which are less than any emissions from
producing, transporting and processing. Conserving forest,
grassland and other non-agricultural vegetation or discourag-
ing further agricultural management practices into new lands
can restrict GHG emissions (Foley et al., 2005).
The net benefit of these practices so adopted will depend on
the combined effects on all gases (Robertson and Grace, 2004;
Schils et al., 2005; Koga et al., 2006), which may either reduce
emissions indefinitely or temporarily (Marland et al., 2001,
2003a; Six et al., 2004). Where a practice affects radiative forc-
ing through other mechanisms such as aerosols or albedo, those
impacts also need to be considered (Marland et al., 2003b;
Andreae et al., 2005). The broad categories of options men-
tioned above can be adopted through any one or combination of
the management practices discussed below.
Cropland
management
Mitigation practices in cropland management include the fol-
lowing practices:
