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More accurate soil carbon measurement

Jesse Bussard Published on 13 May 2014
Jim Choquette soil carbon

Soil possesses great potential to sequester atmospheric carbon dioxide. However, according to grazing scientist and consultant Terry McCosker of Australia, agriculture will have to change worldwide before we can successfully sequester this carbon.

McCosker was a guest at the Ranching For Profit School that I attended in Billings, Montana. During his visit he gave a short talk on the potential of soil to sequester carbon and a new agricultural business endeavor he was helping launch, called Carbon Link, to help with this effort.

According to McCosker and Carbon Link, an estimated 1580 gigatons (Gt) of carbon are stored in our earth's soil, more than atmospheric (800Gt) and terrestrial (610 Gt) carbon pools combined. Given this fact, soil is the largest carbon pool over which humans can have influence and offers the most promise as a long-term means to mitigating atmospheric carbon emissions.

"There are two ways to store carbon," he says, "in trees or in soil." Storing carbon in soils is obviously more desirable agriculturally. This addition of carbon increases soil's ability to produce food, hold water, and cycle minerals, while creating greater biodiversity and increased food quality.

Grasslands in particular are home to approximately 30 percent of the world's carbon reserves. Unlike other ecosystems whose carbon is stored in vegetation, 90 percent of the carbon in grasslands is directly located in the soil.

"Carbon gets in soil in two ways," says McCosker. The first is through root exudation, which eventually turns into organic matter. The second involves the carbon pathway of photosynthesis in the plant where fixed carbon is converted into usable sugars.

He explains the plant sends some of these sugars to the roots where they are exchanged with soil microbes for trace minerals that the plant also needs. Mycorrhizal fungi are a critical component of this process, producing a glycoprotein known as glomalin which allows for greater storage ability of carbon in soil.

In the past, science assumed soil's ability to sequester carbon decreased as soil carbon levels rose. Current research, on the other hand, shows higher carbon levels in soil are not reductive as previously assumed. Instead it shows higher carbon levels in soil actually increase soil's sequestering ability. In addition, the period for sequestration in soil may be greater than once assumed, maybe 30 to 40 years.

To promote practices that encourage carbon sequestration, McCosker helped pass the Carbon Farming Initiative in Australia. This initiative allows farmers and land managers to earn carbon credits by storing carbon or reducing greenhouse gas emissions on their land. Through Carbon Link he is taking this initiative one step further by developing systems, services and support to help farmers in Australia measure and profit from the carbon they store.

Of particular interest is the new technology Carbon Link has developed to measure and baseline carbon levels in soil. This new technology is nearly 100 times more accurate than conventional methods and by using it the company was able to take the first-ever large-scale accurate measurement of soil carbon in the world.

The process can take as little as six days or as many as eight weeks to complete and is entirely dependent on the amount of acreage being assessed. There are six steps for measuring soil carbon in Carbon Link's system:

  1. Early survey and feasibility – The extent and economics of a project are determined, which includes aspects such as existing soil carbon, livestock emissions, feed and supplements, fertilizer and above-ground woody biomass.
  2. Stratification – Soil variations are stratified, which helps determine where soil samples should be collected. This may be done by ground or aerial survey or a combination of both.
  3. Soil sampling – Soil samples are taken at locations determined in step 2. High-speed systems are used to take deep soil cores, which improve baseline measurements.
  4. Soil analysis – Samples are analyzed to determine carbon content using a number of advanced screening techniques including gamma radiation, NIR and targeted combustion analysis.
  5. Data analysis and calculating carbon yield – Site ancillary and soil sample data are analyzed to reduce uncertainty and produce detailed 3-D maps of soil carbon.
  6. Soil carbon mapping – 3D maps are distributed to land owners and can be used to understand how to best manage and improve carbon levels in different areas.

What sets Carbon Link's methodology for measuring soil carbon apart from others, says McCosker, is the technology's ability to measure deep soil carbon stores with a low variance. The implications of this means small changes in soil carbon can be more easily detected, making for more proactive management to improve soil carbon stores. In addition, this new technology will allow Australian farmers to be the first in the world to actively trade soil carbon credits by allowing for determining soil carbon baselines and monitoring changes in soil carbon over time.  FG

Jesse Bussard is a freelance writer based in Bozeman, Montana.

Jim Choquette of Upland Nebraska capitalizes on native grasses on his operation. Grasslands store approximately 30 percent of the world's carbon reserves – 90 percent of which is directly located in the soil. Photo by FG staff.