The carbon storage potential of soils has likely been significantly overestimated, according to a study published in Nature Communications this week. The findings indicate that global soils may not store as much organic matter, and thus carbon, as previously thought.

Global soils are thought to provide a carbon sink, where carbon can be safely locked away from the atmosphere for long-periods of time. This is partly achieved by organic matter within the soil ‘sticking’ to mineral surfaces, which slows its decomposition and thus slows carbon release. Indeed, the potential of a soil to store carbon is often predicted based on its clay content. In order to determine if this is a realistic predictor, Cordula Vogel and colleagues monitored an incubated arable soil, with a typical mineral composition of temperature zones, over 42 days and used state-of-the-art instruments to directly visualise the minute organic matter-clay associations. The team report that organic matter stuck only to minerals with rough surfaces, which represented as little as 19% of the visible mineral areas.

The team’s results indicate that clay content should not be used to predict the carbon storage potential of soils and that global estimates may need to be revised.