What's Up at the USDA Office?

Upcoming Deadlines/Dates
October 31: Organic Certification Cost-Share and Transition/Education Certification Program

The Wonderful Smell of Healthy Soil
by LuAnn Rolling, District Conservationist

You may not have heard of geosmin but, wherever you may be on this planet, it is highly likely that you’d recognize its smell.

Geosmin is the soil-based compound that gives the earthy smell so characteristic of spring. It’s the wonderful smell after recent rainfall or while digging in the soil and is also the source of the earthy taste in some vegetables. The human nose is so sensitive to the compound that it is detectable at one hundred parts per trillion.  To put that in context, a shark can smell blood at one part per million. That means human noses are 200,000X more sensitive to geosmin than a shark is to blood.

Geosmin boosts certain chemicals like serotonin and norepinephrine in your brain which act like antidepressants. Rain on healthy soils may decrease stress and improve your mood.  That’s why a good rain can be so refreshing to human mental health. The earthy smell of geosmin is directly related to healthy soil microbes.

It’s not the soil we smell, but the bacteria in the soil that’s producing the chemical that we smell. The smell will be different depending on where the soil is found.  Healthy, productive soils should smell fresh, clean and pleasant or have little odor at all. If the soil smells like ammonia or has a rotten odor that is a good indication there is poor drainage or lack of oxygen in the soil.

But why does this odor exist? New research by scientists in Sweden and the UK has helped to explain why. The secret, according to the study published in Nature Microbiology, lies in an ancestral mutual relationship between the soil bacteria Streptomyces and primitive, six-legged creatures called springtails (Collembola).

Streptomyces are globally significant bacteria that produce a range of organic compounds, including chemical weapons to fight off enemies in the soil such as nematodes. These have been used for human use as some of the world’s most effective antibiotics.

The study finds that geosmin and 2-MIB are chemical signals that guide springtails to Streptomyces as a privileged food source.

Professor Mark Buttner of the John Innes Centre, one of the authors of the study, explains: “There is mutual benefit. The springtails eat the Streptomyces and then distribute the viable spores so the Streptomyces get dispersed.”

So, the next time you walk in the woods or dig in your garden and notice the “smell of spring”, spare a thought for the springtails and Streptomyces toiling in the soil below; an example of chemical communication that’s endured for 450 million years. When we smell that sweet fragrance of soil remember the soil is alive and ultimately it’s the soil that gives us life.