Q. How could U.S. farm policy encourage the farm sector
to reduce greenhouse gases?
A. Crop and grasslands account for 55
percent of all land in the contiguous 48 States, and
given appropriate economic inducements, significant areas
could be managed to increase the quantity of carbon stored
in the soils and above ground biomass (also called carbon
sinks). The options most often discussed for sequestering
carbon in agricultural lands are:
- Shifting areas of marginal cropland and pasture into forests
or natural grasses
- Encouraging adoption of production practices that accumulate
carbon in soil (e.g., expanding no-till, eliminating summer fallow,
and planting winter cover crops).
The Kyoto Protocol left to future negotiation
many details on the ultimate role of terrestrial carbon sinks in
reducing U.S. greenhouse gas (GHG) emissions. Many of these details
are scheduled to be addressed at the 6th Conference of Parties to
the UNFCCC (COP6) in November
2000 and have been the subject of intense preliminary negotiations.
While it is premature to assume particular outcomes for these negotiations,
it is clear that if carbon sinks are to count as offsets to national
GHG emissions, then the affected lands will have to stay in their
new uses for extended periods of time (perhaps a minimum of 20 years).
That is, managing land to sequester carbon for a few years and then
returning it to production, or resuming conventional tillage in
the case of land put into no-till, would quickly release any carbon
that had been added to soils or biomass (ERS, 1998).
Policies to promote carbon sinks in the farm sector will need to
ensure that conditions exist under which producers are willing to
enter relatively long-run commitments regarding land management.
Lands shifted from commodity production to forests or permanent
grasses will mostly generate a net carbon gain. While society may
view this carbon accumulation as beneficial, private landowners
may be unmoved unless policies to promote these forest and grassland
sinks establish economic inducements.
For lands that remain in production, carbon input is affected
by the level of crop residue left on and in the field, which in
turn is a function of crop choice (including rotation system), fertilizer
use, timing of field operations (e.g., planting, harvesting, and
irrigation), and climate. All but climate are largely management
variables. Carbon output is affected by the level of biomass
removed, the rate of biological oxidation, and the rate of soil
erosion. These factors can also be influenced by farm management
decisions. Switching from conventional tillage to no-till, for example,
increases crop residues left on and in the soil (reducing biomass
removal and erosion) and decreases soil mixing (reducing biological
oxidation).
A number of farm management practices,
if widely adopted, could enhance agriculture's role as a carbon
sink. Because these practices vary in their relative potential to
store carbon and in the costs to farmers, a comprehensive approach
to sequestering carbon on agricultural lands will need to use the
full set of USDA conservation policy tools. USDA might also facilitate
emissions trades between farmers and agents in other sectors and
promote production practices that reduce methane and nitrous oxide
emissions (such as cost sharing covered livestock waste lagoons
and precision farming).
References
- Bruce, J.P., M. Frome, E. Haites, H. Janzen,
R. Lal, and K. Paustian. 1998. Carbon Sequestration in Soils.
Soil and Water Conservation Society (July).
- Economic Research Service. 1998. Economic
and Environmental Benefits and Costs of Conservation Tillage.
Report to Congress by the U.S. Dept. of Agriculture, Economic
Research Service, in collaboration with the Natural Resources
Conservation Service (Feb.).
- U.S. Department of Agriculture. 1997. Economic
Analysis of U.S. Agriculture and the Kyoto Protocol. Office
of the Chief Economist.
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