USDA Research Suggests the Amount of Corn Stover Available for Ethanol Production Must Be Reduced to Preserve Soil Quality
The US Department of Agriculture’s Agricultural Research Service (USDA ARS) has undertaken a large-scale, five-year project to determine the amount of crop residues (e.g., corn stover, cover crop) that must remain on the land in order to maintain soil organic carbon (SOC) and sustain production.
The Renewable Energy Assessment Project (REAP), which began last year and runs through 2011, is conducting a series of experiments to estimate the amount of residue needed to maintain soil organic carbon and productivity. Focusing on factors including tillage and residue removal and conducted under several environments, these experiments will measure biomass production, grain yield, and change in soil organic carbon.
There are nine ARS locations participating in REAP in eight states, from Alabama to Indiana to Oregon.
Some initial results already suggest that twice as many cornstalks have to be left in the field to maintain soil organic matter levels, compared to the amount of stalks needed only to prevent erosion. In other words, when factoring in soil quality as well as erosion, the amount of biomass feedstock available for cellulosic ethanol production is cut in half.
As an example, a 213-bushel-per-acre corn yield leaves farmers an average four tons per acre of cornstalks after harvest. Farmers could then harvest about two tons of cornstalks per acre for conversion to ethanol—but only from land with low erosion risks, using little or no tillage. If the same farmers rotate with soybeans as recommended, they can only remove half again as much biomass for ethanol production, or just one ton per acre, to compensate for the lower biomass left by soybeans.
In determining the amount of crop residue required for the conservation of soil quality, REAP is:
Estimating the trade-off between the short-term economic return to growers who harvest crop residues as biofuel or biomass product feedstock versus the long-term benefits to soil, water, and air resources associated with retaining crop residues to build soil organic matter and sequester carbon.
Developing algorithms to guide the amount of crop residue that can be sustainably harvested as feedstock for biomass ethanol and bio-based products without degrading the soil resource, environmental quality, or productivity.
Developing management strategies (e.g., no tillage) supporting sustainable harvest of residue.