In a new study, increased carbon dioxide in the atmosphere has been linked to decreased soil organic matter.
The study was conducted at the U of I's (University of Illinois) SoyFACE facility - an open-air laboratory by soil scientist Michelle Wander.
Wander, in her study, expected that increased carbon dioxide in the atmosphere would increase plant growth, increase plant biomass and ultimately beef up the organic matter in the soil.
But what the research team found instead was that organic matter decay increased along with residue inputs when carbon dioxide levels were increased and according to them, the accelerated decay was due to increased moisture in the soil.
"Going into the study, the assumption was that higher levels of carbon dioxide in the atmosphere will increase crop yield and soil organic matter," said Wander.
"We did see a 30 percent increase in above- and below- ground soybean biomass so we expected that to be mirrored in soil organic matter, but there wasn't an increase. In fact, organic matter levels may have even been lower than in plots not exposed to elevated carbon dioxide levels," she added.
According to Wander, most models or projections of the future assume the carbon dioxide fertilization effect would be a good thing for agriculture and the world's food supply and have a benefit to soil organic matter.
"But more and more, we are finding things are a little more complicated. What our study shows is that in this system, rising carbon dioxide levels are not contributing to soil health after all," he said.
The researchers suspect soil moisture plays a role in this phenomenon.
When plants take up moisture, they open their stomata - the pores through which they transport both carbon dioxide and water and when plants satisfy their need for carbon dioxide, they can close those stomata and conserve water.
"This appears to have happened at SoyFACE in both corn and soybean crops. So, moisture feedbacks that increased microbial activity might solve the mystery," said Wander.