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 to maintain soil organic carbon (SOC) and sustain production.
The Renewable Energy Assessment Project (REAP), which began last year and runs through 2011, is using a series of experiments with factors including tillage and residue removal conducted under several environments to measure biomass production, grain yield, and change in soil organic carbon, and from these measurements to estimate the amount of residue needed to maintain soil organic carbon and productivity.
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.
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