ARS scientists help improve soil carbon calculations

July 4, 2014 by Ann Perry
ARS Scientists Help Improve Soil Carbon Calculations
ARS scientists have identified factors affecting the measurement of soil carbon sequestration, which is important in assessing how farming practices can reduce carbon emissions. Credit: NRCS-USDA.

A potential source of error in calculating soil carbon budgets has been identified by scientists at the U.S. Department of Agriculture (USDA).

Agricultural Research Service (ARS) soil scientist Hero Gollany has used these findings to refine methods for assessing farming practices that retain carbon in the soil and thus mitigate carbon emissions that contribute to global . ARS is USDA's chief intramural scientific research agency, and these findings support the USDA priority of responding to climate change.

Rates of soil carbon retention, known as sequestration, are often measured and estimated by tracking changes in total soil carbon over time. Carbon from crop residues or other decaying plant material is present in soil samples collected for these sequestration studies. But this "accrued" carbon is not actually sequestered in the soil until after the carbon becomes attached to soil mineral particles, a process that can take several decades.

Until that happens, the accrued carbon from decomposing can readily be lost from the soil, because it is not bound or associated with soil particles. Inadvertently adding the accrued carbon to measurements of sequestered carbon results in overestimates of how agronomic practices affect sequestration levels.

Gollany and Washington State University soil microbiologist Ann-Marie Fortuna used data from another soil carbon field study to see how levels of a specific type of carbon called "light-fraction" carbon affected measurements. Using this method, the scientists determined that levels measured in the study included carbon from fine crop residue materials that passed through sieves during sample processing—carbon that had accrued in the soil, but was not yet sequestered via decomposition.

This accrued carbon ranged from 13 percent to 19 percent of the total in the samples. This, in turn, skewed attempts to use carbon data from the samples to model levels.

Gollany, who works at the ARS Soil Conservation Research Unit in Pendleton, Oregon, published her findings in 2013 in the Soil Science Society of America Journal.

Explore further: Carbon sequestration not so simple in biomass crop production

Related Stories

Carbon sequestration not so simple in biomass crop production

February 21, 2014

Findings at the U.S. Department of Agriculture (USDA) are providing information about the soil carbon dynamics that play a crucial role in lifecycle assessments of bioenergy production. These studies at the Agricultural Research ...

Farming commercial miscanthus

August 31, 2011

An article in the current issue of Global Change Biology Bioenergy examines the carbon sequestration potential of Miscanthus plantations on commercial farms.

Kudzu can release soil carbon, accelerate global warming

July 1, 2014

Clemson University scientists are shedding new light on how invasion by exotic plant species affects the ability of soil to store greenhouse gases. The research could have far-reaching implications for how we manage agricultural ...

Large soil carbon stores trigger rethink

September 24, 2013

WA researchers will soon examine if carbon stocks found metres down in soil is inert or active after a study found significantly more carbon stored than previously thought.

Recommended for you

Synthetic chemicals: Ignored agents of global change

January 24, 2017

Despite a steady rise in the manufacture and release of synthetic chemicals, research on the ecological effects of pharmaceuticals, pesticides, and industrial chemicals is severely lacking. This blind spot undermines efforts ...

New findings on carbon cycle feed climate research

January 23, 2017

A Florida State University researcher is taking a deep dive into the carbon cycle and investigating how carbon moves from the ocean surface to greater depths and then remains there for hundreds of years.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jul 07, 2014
I am not sure how relevant this study is to the issue of measurement of overall soil-carbon sequestration. As I understand it, carbon in soil is always coming and going and what is important, both for sequestration and for agronomic purposes, is the equilibrium level. This level can be increased by either increasing the rate of flow of carbon into the soil or by reducing its rate of loss (or both). From this perspective, it doesn't matter if the carbon has been stabilized, as long as the changes in rate of flow are permanent (e.g., the management practices are maintained). If they are, the equilibrium point will move to a higher level (e.g., 3% instead of 2%), and for all intents and purposes the soil will have sequestered that amount of carbon. Perhaps I am not understanding this correctly. I would like to hear what others think.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.