Robert C. Brown is Bergles Professor of Thermal Sciences in the Department of Mechanical Engineering at Iowa State. He is also director of the Center for Sustainable Environmental Technologies and the Office of Biorenewables Programs. His research team has recently been notified that this project will be sponsored by the U.S. Department of Agriculture.
Point of Departure: Reinventing Agriculture for Environmental Enhancement
“We can reinvent American agriculture in a way that doesn’t just minimize its impacts on soil, air, and water, but actually enhances the environment.”
by Robert C. Brown
North America’s prairies are among the world’s greatest natural resources for the production of food and fiber. Before agriculture, however, they were also gigantic sinks for carbon dioxide sucked from the atmosphere by forbs and grasses and stored underground—one of nature’s processes for sequestering greenhouse gases.
The sodbusters changed all that. Their plows ripped up the prairie, subjecting the exposed soil to erosion, washing and blowing its fertility elsewhere at the rate of five tons per acre per year. Agriculture had the further effect of exposing soil carbon to oxidation, releasing carbon dioxide into the atmosphere where it contributes to global climate change.
Iowa is thought to have lost half its soil carbon since cultivation began 150 years ago. That number is open for debate, but it is generally recognized that, as currently practiced, agriculture is slowly depleting soil fertility.
Good land stewardship minimizes the negative impacts of agriculture. But this alone is not enough to pass the test of sustainability, which requires that natural resources be employed in a manner that assures their availability for future generations. Modern agriculture’s reliance on fossil fuels to power tractors and produce nitrogen fertilizer, as well as its role in the depletion of topsoil and soil carbon, add up to a less than stellar record of sustainability.
We can reinvent American agriculture in a way that doesn’t just minimize its impacts on soil, air, and water, but actually enhances the environment, a “new” agriculture inspired by the pre-Columbian peoples of South America.
Recent archaeological studies in the Amazon basin have revealed that the highly oxidized, infertile soils common in this region are interspersed with well-defined areas of highly productive soils. Known as Terra Preta (“dark earth”), they are substantially darker than surrounding soils and contain large amounts of charcoal and pottery shards. These anthropogenic soils were created by indigenous people through the gradual addition of manure and charcoal formed by burning plant material.
Thought to arise from the increased biological activity of bacteria and fungi colonizing the porous char, these soils have remarkable fertility compared to untreated soils in the same locations. Furthermore, this carbon appears to have been stably sequestered as soil organic matter for hundreds if not thousands of years.
Could we duplicate these results, yielding a system that not only produces food crops but also rebuilds soils, meets the energy demands of modern agriculture, and sequesters greenhouse gases from the atmosphere?
Iowa State is studying the feasibility of just such a system for corn production. In this system, about half the stover (the residue of stalks, leaves, husks, and cobs) is harvested along with the grain. The stover is then partially burned to form charcoal and an energy-rich liquid known as bio-oil, which is reacted with steam to form hydrogen in lieu of the natural gas typically used to manufacture fertilizer. The ammonia and charcoal are then injected into the soil to serve as a nitrogen fertilizer, a biologically active soil amendment, and a carbon sequestration agent.
In effect, the farmer provides all of the energy to manufacture fertilizer for his own farm. Using stover to manufacture ammonia, a 640-acre corn operation would save one million cubic feet of natural gas annually and would avoid releasing 65 tons of CO2 into the atmosphere. The farmer would also receive a fuel credit equal to about 50% of the cost of anhydrous ammonia.
While switching from conventional tillage to no-till would sequester only about 310 tons of carbon dioxide per year, the charcoal produced by this farm would effectively sequester 1,800 tons—the annual tailpipe emissions from 340 automobiles. Although their value in the U.S. is only speculative at this time, carbon credits in international markets average about $3.50/ton, or $6,900 for a 640-acre farm.
Not least among these benefits is the anticipated improvement in soil quality as a result of the application of char. And though these results have not been fully demonstrated, the experience of the pre-Columbian peoples of the Amazon basin—not to mention the futures of our children and the land—encourages this attempt to reinvent agriculture.