This graph shows how different farming methods affect soil carbon  in surface soils (to~8 inches deep). Soil samples were collected in 2001, 12 years after the systems were established. Before this, there were no differences in soil carbon levels across the different systems. Annual field crops were a rotation of corn, soybeans, and wheat. Treatments with different lower case letters above them are statistically significantly different (p ≤ 0.05). Adapted from Syswerda et al. 2011.

Soil organic matter, also called soil carbon, is  important to farmers because it contributes to  soil quality and crop productivity. Soil organic matter provides plants and soil organisms with the nutrients they need to grow. It also influences  soil physical properties such as drainage and structure and a soil’s water holding capacity, all of which help create a good environment for crop roots and boost yields. Soil organic matter levels in crop fields are also linked to global climate change, an issue that extends far beyond the farm field. Agricultural lands have the potential to mitigate—reduce the severity of—global climate change by storing carbon as soil organic matter and thereby kept out of the atmosphere. This is commonly referred to as soil carbon sequestration.

This graph shows how various farming methods affected the amounts of carbon in surface soils at the Kellogg Biological Station Long-term Ecological Research site. As this data shows, there are ways of farming the land that promote soil carbon sequestration. For annual cropping systems such as corn, soybean, or wheat, growing plants without plowing using no-till technology allows carbon to accumulate in soil rather than be transformed to CO2 by microbes. Plowing causes the soil layers mix with air, resulting in accelerated soil microbial activity. This accelerated activity causes soil organic matter (formerly crop residue) to be broken down more quickly and its organic carbon to be converted to carbon dioxide, which escapes to the atmosphere. Under no-till farming, the soil remains undisturbed and organic matter can accumulate faster than it decomposes, resulting in soil carbon gain.

Because changes in soil carbon occur slowly, scientists track soil carbon levels in a given area over many years to document changes. To date, most estimates of how much carbon sequestration could occur from agricultural lands have been based on studies of soil carbon change in surface soils—the top 6 inches or so. KBS LTER measurements, in contrast, extend to 1 meter, which includes most of the plant rooting zone.

KBS researchers use a geoprobe to collect deep soil samples from the LTER plots.

In 2001, KBS researchers collected many soil samples to depths of three feet from plots that had been under different types of farm management for 12 years. The researchers discovered that amounts of surface soil carbon were greater under no-till management compared to the conventional cropping system that included plowing, and that there was no change in soil carbon at greater depths. These findings demonstrate that no-till farming can sequester carbon and provide climate change mitigation—good news for both farmers and society. But KBS researchers have also learned that if land that has been under no-till farming is eventually plowed, it loses all of the carbon it had gained. KBS LTER researchers are now analyzing a second decade of soil carbon change. These new findings will continue to help farmers and policymakers manage and develop agricultural landscapes that provide high crop yields and environmental protection.

For Further Reading

Syswerda, S. P., A. T. Corbin, D. L. Mokma, A. N. Kravchenko, and G. P. Robertson. 2011. Agricultural management and soil carbon storage in surface vs. deep layers. Soil Science Society of America Journal 75:92-101.

Grandy, A. S. and G. P. Robertson. 2007. Land-use intensity effects on soil organic carbon accumulation rates and mechanisms. Ecosystems 10:58-73.

Paul, E. A., A. Kravchenko, A. S. Grandy, and S. Morris. 2015. Soil organic matter dynamics: controls and management for sustainable ecosystem functioning. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural landscapes: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA.

Ruan, L., and G. P. Robertson. 2013. Initial nitrous oxide, carbon dioxide, and methane costs of converting Conservation Reserve Program grassland to row crops under no-till vs. conventional tillage. Global Change Biology 19:2478-2489.

For Further Information: Dr. Phil Robertson (

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