Growers and scientists continue to improve the future
Discussions of climate change abound these days; one collaborative effort is taking positive steps to help growers mitigate agriculture’s role in the issue. Although most of the greenhouse gases thought to be warming the earth originate from burning fossil fuels, agriculture is a primary source of methane and nitrous oxide emissions to the atmosphere; however, the farming community is already taking action to reduce the impact.
Carbon dioxide is trapped by green plants and stored in their tissues through the photosynthesis process. Organic carbon is captured within soil but methane and nitrous oxide can escape. Farming practices, such as tilling, water and fertilization applications, and crop selection, can modify the amount of those discharges. Determining the optimal techniques is the work of a selected group of Agricultural Research Service [ARS] scientists.
What is GRACEnet?
A team of more than 60 researchers, spread across the country in 32 ARS stations, forms a group known as GRACEnet (Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network). The ongoing project is comparing traditional and alternative farming systems to evaluate their efficacy in reducing greenhouse gases and sequestering, or capturing, carbon in the soil.
Jane Johnson, a research soil scientist stationed at the North Central Soil Conservation Research Laboratory in Morris, Minn., says the GRACEnet concept was born at a 2002 global change national program meeting. Scientists collaborated to develop common protocols for measuring and documenting soil carbon and greenhouse gas emissions and information sharing. The project launched its first five-year research cycle in 2005.
Goals of the project
In addition to developing the most effective ways to trap carbon in soil and to reduce gas emissions, the scientists seek to determine the environmental effects (water, air and soil quality) of those systems. Johnson adds that those goals grew out of a desire to identify economically, agronomically and environmentally sound methods to curtail global climate change and provide environmental benefits. Recognizing that economics would play a crucial role in the adoption of proposed practices, recommended strategies must be feasible for agricultural production—no unrealistic scenarios allowed.
Other expected outcomes include national and regional guidelines for soil conditioning and computer models for measuring management practices’ effect on gas emissions and soil carbon storage.
Maximizing the efficacy
GRACEnet was planned for maximum efficacy and the nationwide nature of the ARS facilitates this goal. Utilizing research stations across the country will result in recommendations appropriate for differing climatic conditions and various agricultural segments.
Each station’s work, whether soil analysis, air or water quality or gas emissions, is customized to a “business as usual” model. In other words, the research is based upon the agricultural segment commonly practiced in that region and incorporates its typical climatic conditions and farming standards. Within those parameters, each location seeks optimal methods for maximizing soil carbon sequestration and environmental benefits and minimizing greenhouse gas escape.
“Carbon sequestration may well become part of a larger conservation benefit package,” Johnson adds. “Land managers and policy makers are interested in tradeoffs among management options.” Some research stations are studying the impact of carbon sequestration on air, soil and water quality. Those findings may lead to conservation agencies’ heralding new action plans.
Shadowing the researchers
Now into the final year of the initial five-year research cycle, scientists are sharing some preliminary results of GRACEnet’s work. Although widespread, concrete recommendations aren’t yet available, early findings may indicate future trends for growers’ operations.
In Johnson’s research, the business as usual scenario is corn/soybean rotation with aggressive tillage. For study purposes, a four-year crop rotation of corn, soybean, wheat with alfalfa and perennial alfalfa was coupled with significantly reduced tillage [strip, or shallow, tillage after alfalfa and corn] with the goal of maximizing carbon sequestration. An additional study was aimed at reducing gas emission by withholding fertilizer from the same crops. Recommended nitrogen management was maintained in all cases.
During three years of emissions monitoring, the impact on nitrous oxide was small, which Johnson attributes to the nitrogen use. Initial analysis suggests all three scenarios were carbon neutral, and concludes that the maximum carbon sequestration strategy was carbon negative. Highly variable soils in the station’s western Minnesota location make evaluating the carbon results difficult.
At the Crop Systems and Global Change Lab in Beltsville, Md., scientists are working with automated soil carbon dioxide flux chambers to monitor and track changes. Experimenting with maize, soybean and wheat, preliminary findings demonstrate that tillage affects bulk density, but not on soil carbon or crop yield, and nitrogen affects crop yield in maize and wheat. In the spring of 2008, researchers observed that nitrogen and tillage affects soil carbon dioxide flux prior to preparation for planting.
In Auburn, Ala., the effects of elevated carbon dioxide on the atmosphere are being studied in relation to both crops and grazing. Scientists are finding that soil carbon dioxide release is increased by approximately 50 percent by both elevated levels and conservation management.
A Nebraska study is looking at the effects of transitioning longtime bromegrass fields to producing corn for biofuels. In the 1990s, grass was commonly used to prevent soil erosion and maintain soil carbon. In fact, farmers were urged, in some cases with cash payments, to establish grass crops. In more recent years, a growing interest in biofuels has brought some farmers back into corn production.
In the experimental plots, corn was grown using no-till methods and chemical weed management. Soil organic carbon is being monitored regularly. Prior findings indicated that returning to corn would significantly reduce carbon, with the assumption of heavy tilling.
The GRACEnet-related work, however, refuted that theory, finding that no-till methods did not decrease organic carbon significantly at any soil levels. The result has been replicated over several seasons, during periods of drought, which may have been expected to increase carbon release.
In eastern Oregon, where soil carbon levels typically are low, strip tillage has been demonstrated as a viable method for building higher carbon levels. Pendleton, Ore., researcher Hero Gollany is also involved in making computer models more user-friendly, to offer growers an effective tool in soil management.
Future strategies for growers
GRACEnet’s accomplishments to date are paving the way for future agricultural practices. It is becoming clear that, according to an ARS global change report, soil conservation practices such as decreasing tillage intensity (volume of disturbance), increasing surface residue retention and crop diversity are associated with increased soil organic carbon and improved soil quality. Manure may reduce greenhouse gas release by improving carbon sequestration; however, such treatments must be managed to avoid run-off and increase nutrient availability. Techniques that increase soil organic carbon content may also benefit soil water infiltration and nutrient cycling, while reducing erosion concerns.
Johnson says that GRACEnet research aided in the development of a carbon credit program for the National Farmers Union (NFU) in collaboration with the Chicago Climate Exchange. The NFU program has expanded to include 25 states in the U.S. with a total enrollment (in 2006 and 2007) of 2.54 million acres. The NFU initiated a carbon credit program for native rangeland in 2007.
“These carbon credit programs have the potential to realize multiple benefits for agricultural producers, including increased farm income and improvements in soil quality, while concurrently mitigating agriculture’s impact on global climate change,” she adds.
While these studies continue, Johnson says there are general steps growers can take today to help mitigate agriculture’s role in climate change. Nitrogen management techniques, such as reducing leaching, runoff or volatilization, reduce nitrous oxide formation. Employ practices that maintain and/or build soil organic matter, which is more than 50 percent carbon. Effective techniques include no tillage (or reducing the volume of soil disturbance) and adding cover crops or living mulches. For recommendations specific to your crop, climate and region, consult with local soil conservation agencies.
Based in Greensboro, N.C., the author writes articles about horticulture, landscaping, agriculture and travel. She has been a contributor to Moose River Media publications for three years.