Newswise — ITHACA, N.Y. – Soil scientists from Cornell and Rice Universities have dug around and found that although adding carbon organic matter to agricultural fields is usually advantageous, it may muddle the beneficial underground communication between legume plants and microorganisms.

In a symbiotic relationship, microbes called rhizobia act like agricultural ‘butlers’ to fetch nitrogen from the air for the legume plants. When carbon is added to the soil, it helps the soil retain nutrients, but it can repress plant-microbe communication by up to 70%, according to new research published in Science Advances.

“The communication connection gets a lot of static, you might say,” said Johannes Lehmann, professor of soil and crop sciences and senior author. “With carbon amendments to the soil, the plants and the microbes cannot chemically communicate as well anymore. They can’t ‘hear’ each other.”

For more than a century, scientists have known about the symbiotic relationship between legumes and rhizobial microorganisms. To help the soil’s microorganisms and plants interact, flavonoids (plant and fungus metabolites) act as chemical ‘telephones,’ but higher amounts of organic carbon – such as compost or wood chip mulch – in the soil hinder that communication.

For additional information, see this Cornell Chronicle story.

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