Soils treated with organic fertilizers store more carbon, study finds

As carbon dioxide levels in the atmosphere have increased in recent decades, the need for strategies to capture and retain carbon has become increasingly urgent.

Researchers at Kansas State University (K-State) are studying how different farming practices can affect the amount of carbon stored in soil. Using the Canadian Light Source (CLS) at the University of Saskatchewan (USask) and the Advanced Light Source in Berkeley, California, they analyzed soil from a Kansas cornfield that had been grown no-till for the past 22 years.

During this period, the farm used different soil nitrogen management practices, including no fertilizer, use of chemical fertilizers, and use of manure/compost fertilizers. The results are published in the Journal of the American Society of Soil Scientists.

“We were trying to understand the mechanisms by which we can increase carbon storage in the soil using certain management practices,” said Dr. Ganga Hettiarachchi, professor of soil and environmental chemistry at Kansas State University. “We were not only looking at soil carbon, but also at other minerals in the soil that are going to help store carbon.”

As other studies have shown, the University of Kansas researchers found that soils treated with manure or compost stored more carbon than soils that received either chemical fertilizers or no fertilizer. But what’s even more interesting, Hettiarachchi says, is that the ultra-bright synchrotron light allowed them to see how the carbon was stored: They found that it was held in the pores and that some of the carbon had become attached to soil minerals.

The team also found that soil treated with manure or compost contained more microbial carbon, indicating that these improvements promote more microorganisms and their activities in the soil. In addition, they identified special minerals in the soil, which Hettiarachchi says proves that the treatments contribute to active chemical and biological processes.

“To my knowledge, this is the first direct evidence of the mechanisms by which organic amendments improve soil health, microbial diversity and carbon sequestration.”

Because synchrotron imaging is nondestructive, the K-state researchers were able to observe what was happening in soil aggregates (clods) without having to break up the soil; essentially, they were observing carbon chemistry in its natural state.

“Collectively, studies like this will help us move toward more sustainable and regenerative agricultural practices that will protect our soils and environment while helping to feed a growing population,” Hettiarachchi says. “Additionally, understanding the role of different minerals, chemicals, and microbes involved will help improve predictive models of how different agricultural practices affect soil carbon storage.”