Agriculture Reference
In-Depth Information
For Scenarios 2, 3 and 4, the annual GHG emission changes had to be
compared to changes in soil carbon under both ∆ cA and ∆ rA. The payback
periods in years required for reductions in annual GHG emissions to equal
the 40 year cumulative losses in the soil carbon stock were determined
from the ratios of the 40 year soil carbon losses (rows 1 to 3) to the respec-
tive decreases in annual GHG emissions (rows 4 to 6).
The largest loss of soil carbon came from reseeding all of ∆rA to an-
nual crops (Scenario 2, Table 6). The lowest loss in soil carbon results
from leaving all of the residual land under perennial ground cover without
repopulating ∆rA with beef cattle (Scenario 1). Repopulating ∆ rA with
just a category of beef that is highly forage dependent (Scenario 4) re-
sulted in slightly less soil carbon loss than from repopulating ∆ rA with
beef cattle fed a mix of forage and grain (Scenario 3) in both eastern and
western Canada. The net annual GHG emission reductions for Scenarios
3 and 4 are appreciably lower than the net annual emission reductions in
Scenarios 1 and 2. The negative result for the eastern emission quantity for
Scenario 4 indicates a net increase in annual GHG emissions. Because this
scenario resulted in a loss of GHG mitigation potential in the east, there
was no need to relate this annual loss to the loss of soil carbon.
Due to high methane emissions, payback periods were the highest for
Scenario 4, even though the predominantly forage based cattle produced
the second lowest decrease in soil carbon. The payback period for reseed-
ing all residual perennial forage to annual crops (Scenario 2) was 13%
longer than the mixed forage and grain fed beef herd (Scenario 3) in west-
ern Canada, but was only 40% as long as in the east. Due to the increase
in annual GHG emissions in the east under Scenario 4, no payback period
was shown for this case. For Scenario 3 in the east, the payback period was
2.3 times the 40 year benchmark period. In western Canada, the two ratios
of payback to benchmark periods were 0.7 and 1.4 for Scenarios 3 and 4,
respectively. For Scenario 2, the payback to benchmark period ratios were
1.0 and 0.8 for eastern and western Canada, respectively. For Scenario 1,
the ratios were less than 0.1 for both eastern and western Canada. The very
short payback periods for Scenario 1 were the result of the lowest change
in soil carbon of any of the four Scenarios, as well as the unreduced GHG
savings from the basic beef to pork redistribution.
