The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 318

potential in agriculture at the regional level (in this case Europe) that we
consider here.
Importance of the 1990 Baseline
A number of options for carbon mitigation in European agriculture have
been examined including: (i) switching all animal manure use to arable
land; (ii) applying all sewage sludge to arable land; (iii) incorporating all
surplus cereal straw; (iv) conversion to no-till agriculture; (v) use of surplus
arable land to extensify one-third of current intensive crop production
(through use of one-third grass-arable rotations); (vi) use of surplus arable
land to allow natural woodland regeneration; and (vii) use of surplus arable
land for bioenergy crop production. For estimates made before Kyoto, no
baseline was in existence.
Smith et al . (1997a,b, 1998) quantified the carbon mitigation options
in agriculture in the European Union and the wider Europe, but these were
not set relative to a baseline condition (see Fig. 4.13.2a). The inclusion of a
1990 baseline allows the carbon mitigation potential of each estimate to be
assessed more accurately (see Fig. 4.13.2b).
Other changes between pre-Kyoto and post-Kyoto estimates which
affect the values presented in Fig. 4.13.2a and 2b include: (i) the use of
variable application rates of organic amendments instead of a fixed rate
(e.g. animal manure; see also Smith and Powlson, 2000); (ii) a revision of
the magnitude of the impact of various management changes on soil
organic carbon (SOC; e.g. sewage sludge and natural woodland regenera-
tion); (iii) changes in the agricultural land areas assumed to be available for
changes in land use (e.g. a reduction in the predicted level of setaside by
2010 affecting extensification, natural woodland regeneration and
bioenergy production scenarios); and (iv) changes in the scenarios them-
selves (e.g. the inclusion of two separate scenarios for dedicated bioenergy
production and natural woodland regeneration, replacing the combined
scenario of Smith et al ., 1997a,b).
In addition, combined options can be examined. Smith et al . (2000)
examined combinations of scenarios and showed that there is considerable
potential in agriculture for carbon mitigation (see Fig. 4.13.3). A number of
the combined scenarios were able to achieve EU emission reduction targets
by themselves.
Improving our Regional Projections of Carbon Mitigation
Potential in Agriculture
There are many sources of uncertainty in projections such as those
presented above. One source of uncertainty arises from the method of