Cropping super-sequestration options pack big carbon wallop

Research with degraded soils, enhanced grazing and tree-crop combinations raise expectations of nature’s regenerative potential

By Krista Hozyash 

Biological carbon sequestration  happens on land, water Through the carbon cycle, storage of carbon is possible in oceans, forests, croplands, grasslands and rangelands acting as natural carbon sinks. Approximately half of annual total CO2 emissions are absorbed from the atmosphere into vegetative biomass, soil organic matter and dissolved organic compounds in water. In the United States, current land use practices remove approximately 0.8 billion metric tons of CO2  from the atmosphere for storage every year. The potential of biological carbon sequestration in the country is huge, with 40 billion to 60 billion metric tons of CO2 sequestration possible over the next fifty years at an annual rate of approximately 1 billion metric tons (1.1 billion US tons)  of CO2 Where can the carbon go? Research assembled by the Congressional Budget Office suggests multiple land uses are capable of storing carbon in the United States. Forest systems sequester large amounts, with mature never-harvested forests storing 286 to 1,179 metric tons of CO2 per acre. Working forests experiencing rotational harvests accumulate less carbon in soils as storage capacity decreases with disturbance. An average stand of harvestable timber on a 30-year rotation sequesters approximately 203 to 256 metric tons of CO2 per acre. Agricultural systems like croplands, grasslands and rangelands sequester less carbon in soils than natural forests. In the United States, cropland sequestration varies from 56 to 120 metric tons (62 to 132 US tons) of CO2 per acre  Conservation strategies that restore soils and diminish erosion increase sequestration to between 73 and 159 metric tons (80 and 174 US tons) of CO2 per acre. In addition to terrestrial biological systems, the world’s oceans have sequestration potential. Oceans absorbed about 2 billion metric tons (2.2 billion US tons) of CO2 annually for the last several decades. Their ability to sequester carbon is finite – the maximum potential for carbon storage is approaching as ocean chemistry becomes increasingly acidic. Oceans, other natural ecosystems and working lands already store carbon, but investments must be made in biological systems that hold the greatest potential for sequestration to address climate change.

“We’ve not yet begun to sequester,” is the rallying cry for a new group of agriculturists, people who are exploring the addition of soil carbon as a primary goal rather than just an interesting bonus of improving yields and biological health. They are looking at innovative ways to achieve significant net carbon gains by adding a pasture-livestock “crop” to extended rotations, mixing trees with various crops or grazing, and remediating badly deteriorated soils.

Improved farming techniques can fight climate change in many ways. Most have secondary benefits, making farming practices one of the key strategies for enabling our food production to be more biologically efficient, less fossil-fuel dependent, and better suited to consumer demand for health, safety and sustainability.

Climate-friendly practices, in general, work in two basic ways that impact everyone. They can:
• Mitigate damage by cutting emissions of greenhouse gases that seem to increase risk of climate instability
• Biologically sequester carbon and reduce excess loading of carbon dioxide in the atmosphere by intentionally supporting the natural process of photosynthesis.

Within agriculture, a third route outlines ways to maintain productivity in the face of current climate and weather pattern changes, lumped under the heading of “adaptation.” This includes actions such as:

--Tweaking crop selections to cultivars and varieties that grow better under drier or hotter conditions;
--Fighting off new diseases and pests introduced with changed growing conditions;
--Increasing soil organic matter to retain soil moisture in dry times;
--Increasing crop diversity to improve odds crops will succeed with encountered weather extremes;
--Re-integrating livestock on crop farms to increase economic value of forage crops that add organic matter during their phases of rotation.

Super-sequestration options

Improving soil organic matter as a primary focus is a new research strategy, and it remains a relatively untested area in terms of proven techniques that most effectively create lasting results in soils. Reasons to aggressively look for these answers are supported by the realization that agricultural practices that increase soil organic matter and reduce disturbance from cultivation also sequester more carbon. Research assembled by the Pew Center on Global Climate Change estimates that 257 to 807 million metric tons (282 to 888 U.S. tons) of CO₂ per year could be sequestered in U.S. cropland soils under sustainable practices.

These few examples that follow are early indicators of what’s possible. They provide insights into the many ways soil, climate, crops, cover crop mixtures, moisture and husbandry can be innovatively focused to biologically add carbon to soil. One group seriously committed to forwarding this research is the Round Table on Organic Agriculture and Climate Change, formed at the UN Conference on Climate Change. Eight collaborators agreed on research goals as a start to standardizing this process.

Degraded soils hold great potential: Introducing biodegradable organic matter as compost to soils increases fertility and avoids emissions associated with chemical fertilizers. Composting and using green manures have improved soil quality and food security in Egypt, where less than 5 percent of the nation’s land is considered suitable for cultivation. A study on organic farming operations applying compost in the Egyptian desert indicates increased storage by an average of 1.3 metric tons (2,860 pounds) of CO₂  per acre per year for up to 30 years on soils originally poor in organic matter. The soil gained carbon most rapidly in initial years, but continued adding it at a slower rate throughout the period. Supplementing organic matter rich in microorganisms to desert lands reclaimed for food production creates healthy soil from conditions of depleted nutrients and sparse agricultural growth.

Re-integrating livestock on cropland: Mixed farming that incorporates leguminous grassland in ley/arable rotations builds up fertility in soils and improves capacity for carbon storage. Legumes act as a natural fertilizer and produce nitrogen in soils while livestock direct-harvest forage and convert grasses into food. According to Soil Association research issued in  December 2009, a conversion to organic agricultural systems that support grass-fed beef, mutton, poultry or lamb stores over 0.8 UK tones (1,800 lbs.) of CO₂ per acre annually for at least 20 years.

Benefits of organic farming and grazing systems suggest that eating less meat is not the only solution for combating climate change. Steering practices away from intensive production of white meat and grain-fed beef helps offset the impact of livestock methane emissions as operations improve soil quality and avoid artificial petroleum-based inputs. In such systems, carbon storage, economic return and production potential are reached when approximately half of the land is under grass and legumes and half is under crop production, according to the Soil Association report.

What could wood and water really do?   Protecting existing forests and reforesting degraded lands are some of the most effective ways to increase soil carbon. Research conducted by Richard A. Birdsey (1) estimates afforested lands increase annual sequestration by 2.2 to 9.5 metric tons (2.4 to 10.4 US tons) of CO2 per acre, while reforested lands capture 4.0 to 28.0 metric tons (4.4 to almost 31 US tons) of CO2 –equivalent per acre. Managing forests with low impact harvesting techniques and longer rotation cycles reduces disruption of soils and maximizes storage capacity. Reforestation as an expanding strategy is complicated by the need for agriculture that feeds a growing human population. Agroforestry initiatives (synergistically combining crops and trees) maintain agricultural lands and increase sequestration potential. Combining cropland or pastureland with harvestable tree species allows greater above-ground biomass and soil organic matter. Research conducted by S.H. Sharrow (2) and Syed Ismail of Oregon State and Ranga Agricultural Universities indicates well-managed silvopasture systems annually sequester 1.1 metric tons (2,420 lbs.) of CO2 per acre and 0.8 metric tons (1,760 lbs.) of CO2 per acre more than monoculture forests and monoculture pastures, respectively. In regards to oceans, preliminary research suggests a capacity for algae to sequester carbon. Algae may have a large potential for CO2 storage – a theory being tested with developing technologies like algae bioreactors. NASA recently announced such a prototype system it calls the Offshore Membrane Enclosure for Growing Algae (OMEGA) system, working with biological living systems—driven by the need to transition from dwindling and ever-more expensive supplies of fossil fuels towards abundant, sun-powered systems—researchers are exploring new ways of cooperating with the regenerative capacity of nature to reduce negative impacts of food and fiber production for human well-being.

Enhancing pastures: Livestock grazing on pastures for short, intensive pulses enhances badly deteriorated soils. Soil health increases with periodic, well-timed disturbances to the top layer where most microbial activity occurs. Periods of grazing stimulate grass root re-growth and soil biomass additions while improving biological diversity and the development of soil organic matter, also increasing soil carbon storage ability.

Effects of intensive grazing are enhanced by periods of rest and the use of tillage methods that increase oxygen and moisture underground. After creating the Keyline land management system utilizing the Keyline plow subsoiling tool, P.A. Yeomans reported that he produced 10 cm of healthy top soil from originally poor soil on his farm within three years of adopting his “pulsing pasture” techniques in North Richmond, Australia.

Future policy focus

The promise of sequestration was a focus of past climate change discussions. The Kyoto Protocol was adopted in 1997 as countries forged an international agreement that developed targets for greenhouse gas emissions reductions. In Article 3 of the protocol, terrestrial ecosystem sequestration, ocean sequestration and subsurface sequestration in geological repositories were identified as effective strategies for climate mitigation.

Representation of global carbon flow (NASA) Click for larger image.

More ecologically sound and climate-friendly farming can improve food production capacity, economic opportunity and the ecological quality of working lands. Such efforts used with organic practices simultaneously promote healthy soils, healthy foods, healthy people and a healthy planet. Needed to make this process transparent and understandable is an accepted, verifiable measurement system that can document added carbon, and a monitoring process that ensures carbon remains where it is stored. These advances are essential to help farmers see what works in soil carbon storage, and to show citizens what farmers are contributing to a stabilized climate.

Equitable and motivating incentives for soil improvement need to factor in land-use history, crop and livestock species composition and on-going soil health-  all of which impact a farm’s ability to add carbon and keep it biologically stable. However, to practically reduce global greenhouse gas emissions and improve the earth’s carbon sequestration potential in food- and fiber-producing lands, it will be essential to promote innovative new carbon stewardship techniques to farmers who can adopt them.

Krista Hozyash is a communications intern at the Rodale Institute. She recently graduated with a Masters of Environmental Management from Duke University's Nicholas School of the Environment, and plans to aid communities with conservation and sustainability initiatives.

Projections for carbon mitigation potential by type, with estimated differences between $10/metric ton and $30/metric as starting points. Click on the tables for larger images.

Sources

Birdsey, R. A. 1996. Regional estimates of timber volume and forest carbon for fully stocked timberland, average management after final clear-cut harvest. p. 309-334. In R.N. Sampson, and D. Hair.(eds.). Forests and global change: Vol. 2: Forest management opportunities for mitigating carbon emissions. American forests. Washington, D.C.

Buck, Eugene H. and Folger, Peter. “Report: Ocean Acidification.”  Congressional Research Service. 24 April 2009.

Congressional Budget Office. “Potential for Carbon Sequestration in the United States.”  The Congress of the United States CBO. September 2007.

Haile, Solomon G. et al. “Greenhouse Gas Mitigation in Forest and Agricultural Lands: Carbon Sequestration.” University of Florida. September 2008.

Jones, Christine E. “Building New Topsoil.”  Stipa Native Grasses “Changing Landscapes” Forum Armidale. 3 May 2002.

Luske, Boki and van der Kamp, Joris. “Carbon sequestration potential of reclaimed desert soils in Egypt”.  Louis Bolk Instituut & Soil & More International. 2009.

Richards, Kenneth R. et al. “Agricultural and Forestlands: U.S. Carbon Policy Strategies.” Pew Center on Global Climate Change. September 2006.

United Nations. “Kyoto Protocol to the United Nations Framework Convention on Climate Change.”  UN. 1998.

Sharrow ,S.H., and S. Ismail. 2004. Carbon and nitrogen storage in agroforests, tree plantations, and pastures in western Oregon, USA. Agrofor. Syst. 60:123-130.

Soil Association press release: Copenhagen, carbon and cows, Dec. 16, 2009.

Soil Association Briefing Paper: The role of livestock in sustainable food systems