The soil carbon opportunity

Cutting fossil fuel emissions is not enough to avoid dangerous climate change. Too much carbon is already in the atmosphere, and the oceans are continuing to heat. The Intergovernmental Panel on Climate Change stated in 2007 that "Complete elimination of CO2 emissions is estimated to lead to a slow decrease in atmospheric CO2 of about 40 ppm over the 21st century" (about 9% to 1985 levels; see IPCC's 7 Mb pdf file here, section 10.3).

In other words, the strategy of reducing carbon dioxide emissions, by itself, has little effect or leverage on the atmospheric concentrations. By treating global heating as a problem of energy, emissions, or technology alone, we only get to decide whether to wreck our climate slightly faster or slightly slower.

There is a biological side to global warming and the carbon cycle. Carbon is a main ingredient of all life, and of its remains. While planting trees is rightly discounted as a way to reduce atmospheric carbon, we could increase soil organic matter (58% carbon by dry weight) rapidly and cheaply. This will pull excess carbon out of the atmosphere while also enhancing soil fertility, water quality, food quality and human health, and also reducing floods, droughts, and agriculture's dependence on fossil fuels and chemicals.

How it works

Biological processes, such as photosynthesis and respiration, drive 99% of the carbon cycle. There is more carbon in soils than in vegetation and the atmosphere combined. Soil carbon can be more stable than plant carbon (less subject to oxidation or burning).

Good topsoil is rich in organic matter. To create topsoil, combine minerals, air, water, living things in the soil, living things on the soil, and intermittent disturbance such as grazing (we typically overlook these last two). Do not turn the soil over with plows. Because the roots of perennial grasses give off carbohydrates, and periodically die off, carbon-rich topsoil can be formed fastest by grasslands. The cast-off grassroots, and the carbohydrates exuded by these roots, nourish entire underground communities of soil organisms. These interactions over time produce stable organic matter from dead plant material.

Outside inputs are not always required, but management is---working with rather than against biospheric processes such as water and nutrient cycling.

Why this may be surprising news

  1. Soil organic matter is underground and mostly invisible. The processes that form it are not always well understood, and are not part of most people's ecological awareness.
  2. Large economic sectors benefit from our dependence on purchased agricultural inputs rather than on the processes of soil formation, and government policies abet this dependence. The creation of topsoil and organic matter, as well as its connection to the climate problem, was developed by various strands of alternative agriculture, which are outside the major institutions and centers of power.
  3. Most of the measurements and assessments of the soil carbon opportunity by scientists and academics have been done where biosphere or ecosystem processes are dysfunctional, as in many industrial farming systems. The gains in soil carbon reported from these situations are mediocre, suggesting soil carbon as a mitigation strategy only.
  4. Common beliefs such as the following have helped to hide the soil carbon opportunity:
    • microbes don't count, except pests and diseases
    • soil is mainly a geological product, and soil biology or cover is not important
    • water or nutrient availability is a matter of inputs, not biology
    • global warming is basically a pollution problem, and technology is to blame
    • new knowledge is easily and quickly spread, even across disciplinary boundaries, and accredited experts know best.
  5. New instruments, such as remote sensing satellites, and new research are continuing to reveal the huge role of living organisms in biospheric processes. (See Spencer Weart's fascinating account of the discovery of biology by climate science.) Our beliefs tend to lag behind.
  6. The biological formation of soil organic matter is not a technical solution. We prefer technical solutions, and have trouble recognizing the value of biological processes.
  7. The soil carbon opportunity does not fit into the polarized emotion spectrum of the climate debate, in which climate change skeptics and those who want to control carbon emissions attack and ridicule each other.

The opportunity

The development of soil organic matter in cropland and grassland soils in the world could take atmospheric carbon concentrations down to preindustrial levels, if we also quit burning fossil fuels. (See the calculation.) This would require a transformation of agriculture and land management, and of decision making and politics as well---all tending to increase the resilience of local communities.

Much current federal and local policies work against the creation and retention of soil organic matter. The farm bill, federal public lands policies, and state and local policies all have a huge bearing on soil organic matter, as does the structure and function of a carbon market. The newly formed Soil Carbon Coalition would like your help in spreading awareness of the opportunity and in developing sound policies.

Comments

Report from my farm:
Martha Holdridge
West Wind Farm
www.westwindfarm.biz
7209 MacArthur Blvd.
Bethesda, MD 20816

CARBON SEQUESTRATION from MANAGED PASTURES
January, 2008

Over the past five years we have sent West Wind Farm’s soil samples to West Virginia State University’s testing service to do several tests including organic matter tests. From 2002 to 2007 organic matter in 14 tested paddocks increased from 4.1 % to 8.3% (average.) Here are calculations of CO2 and Carbon sequestration based on the increase in organic matter:

YR OM lbs. OM lbs. C lbs. CO2 equivalent
2002 4.1% 13653 8031 29418
2004 7.0% 23310 13712 50226
2007 8.3% 27639 16258 59554

This is based on:
A 2" soil sample,
The top 6 inches of soil weighing 1,000,000 lbs.
Therefore the 2" sample represents 333,000 lbs. of soil
The OM: C ratio being 1.7:1.0 and
CO2 having 27.3% C
All values represent a one acre area

Thus over five years we have sequestered:
59,554 less 29,554 = 30,136 lb. or 15 tons of carbon dioxide per acre
or 16,258 less 8,031 = 8,277 lb. or 4 tons of carbon per acre

MANAGEMENT

1. Our method for achieving this is Management Intensive Grazing (MIG) in the production of our pasture finished beef. In the tested section of our small farm the steers are moved to fresh pasture every day. How does this frequent moving achieve carbon sequestration? Cattle come into a paddock when the grass is about 8 to 10 inches high. At that time the grass roots are also about 8 to 10 inches long. When our steers eat the grass down to about 2 to 4 inches, the roots also die back to about 2 to 4 inches, leaving behind decomposing roots that become organic matter. And that organic matter is about 59% carbon.

2. Our steers return to a paddock after both the above-ground grass leaves and the below-ground roots are again 8 to 10 inches long. The rest period may be two to 4 weeks depending on rain and other factors. One may think of this system as pulsing the grass, or it may be called rotational grazing. This pulsing may take place 4 to 6 or 8 times over the warm-weather growing season. By means of photosynthesis, with each rotation more CO2 in the air is drawn into the ground as carbon.

3. Another favorable factor may be that we use no chemical fertilizers, no herbicides, no pesticides; some say that this increases carbon sequestration.

MEASUREMENT

Some carbon offsets (e.g. trees) are difficult to estimate before the project or to measure after the practice is completed. I believe the above illustrates that managed pasture is one type of carbon offset with which results can be measured with considerable accuracy both during and after the project.

PRESS

In the general press there is much talk of carbon sequestration by planting tree seedlings and some talk about no-till farming, but so far there has been virtually no talk of utilizing MIG pasture management and the periodic pulsing of pastures to sequester carbon.

Thanks Martha for the informative, succinct report. And let us know if you do any deeper sampling.

Really interesting information i knew about vegetation and carbon but never thought about the soil, we compost anything we can not really for a garden or anything but just to keep waste out of landfills and help the environment. A few months back we swapped all our lights to CFLs, and are currently double glazing our windows once finished were having more insulation added through out the house and come winter time we'll be saving quite a bit on our utility bills and all around reducing energy usage.

Martha, The increase from 4.1% O.M. in 2002 to 8.3% in 2007 interests me. I assume this to be with loss on ignition at 360 degrees or as high as 400 degrees for a sample in the top 6 inches. The increase in that time period might be realistic enough, (given what John Jeavons does with bio intensive gardening), but what come to mind is IS THERE A CEILING TO THE INCREASE DUE TO OXIDATION ? The cap and trade payments for MIG might work for the early C sequestriation but top out it management protocols encounter a limit of oxidation. My specialty is the study of desert soils as affected by grazing. I have a lot to learn of temperate soils. Sincerely, Richard Strong, voiceofthesoil@juno.com

Hi Martha, Richard Strong again regarding depth and O.M.. Paul Zenke of UC Berkeley Forestry,(no longer living), had collected the active C in the top square meter of soils for the entire world. It was his life's work. subsummed in those figures is the distribution within the profile. I wonder what the distribution would be between the active and passive C. I notice Elaine Ingham (Spelling wrong I think), separates out the passive C as "humified O.M. is stable because large complex molecules cannot be decomposed by soil organisms". If my loss on ignition temperature is only 360 degrees in monitoring sequestering C, I'm only measuring the active C and not the passive. There are various levels of C turn over times that range from years to centuries.

The question that is important is, how much time is required for C to move from active to passive storage?