Farming for Ecosystem Services - The Ecology of Agricultural Landscapes - page 41

systems—had exceedingly small annual leaching rates of 0.1-1.1 kg N ha −1 ,
although that was, in part, due to very low or nonexistent rates of nitrogen fertilizer
use. In a related experiment, a perennial cereal crop fertilized at agronomic levels
leached 80% less nitrate than did its annual analog (Culman et al. 2013).
Providing Greenhouse Gas Mitigation
Agriculture is directly responsible for ~10-14% of total annual global anthropo-
genic greenhouse gas emissions (Smith et al. 2007). This is largely the result of
nitrous oxide (N 2 O) emitted from soil and manure and from methane (CH 4 ) emitted
by ruminant animals and burned crop residues. Including the greenhouse gas costs
of agricultural expansion, agronomic inputs, such as fertilizers and pesticides, and
postharvest activities, such as food processing, transport, and refrigeration, bring
agriculture's footprint to 26-36% of all anthropogenic greenhouse gas emissions
(Barker et al. 2007). Mitigating some portion of this footprint could therefore sig-
nificantly contribute to climate stabilization (Caldeira et al. 2004), as might the pro-
duction of cellulosic biofuels if they were used to offset fossil fuel use (Robertson
et al. 2008).
Global warming impact analyses can reveal the source of all significant green-
house gas costs in any given cropping system and, therefore, the full potential for
management to mitigate emissions. Such an analysis for KBS LTER cropping sys-
tems over a 20-year time frame (Fig. 2.4; Gelfand and Robertson 2014) shows how
the overall costs can vary substantially with management. The Conventional annual
cropping system had a net annual global warming impact (in CO 2 equivalents) of
Figure 2.4 . Net global warming impact (GWI) of cropped and unmanaged KBS LTER
ecosystems. Annual crops include corn-soybean-wheat rotations. Redrawn from Robertson
et al. (2014).