Earthworms: Do They Help or Hurt in Terms of Climate Change?
Every once in a while I come across something in the scientific literature that really surprises me. Because there isn’t much oxygen in a worm gut, it creates the ideal conditions for these particular microbes (“de-nitrifiers”) to turn nitrate (NO3) into nitrogen gas and also generate some nitrous oxide in the process.
Ok, some background. Nitrous oxide (N2O) is a very potent greenhouse gas with 310 times the global warming potential of carbon dioxide. Its really an Achilles heel for agricultural sustainability because around 80% of the human-generated emissions of this gas come from farms. If even a small amount of the farmer’s nitrogen fertilizer gets converted to N2O it becomes a major part of the total carbon footprint of that field
As the Worm Turns
We generally think of earthworms as a sign of a good, healthy soil because they are beneficial in creating channels in the soil for air and water to move. One good thing about the very sustainable form of farming called no-till is that when it is practiced, earthworm populations increase. But what about this N2O issue? One scientists calls worms a “mobile anoxic microzone” and another estimates that one third of the N2O released from a soil is generated inside of worms.
Not to Worry
So I scanned the scientific literature about nitrous oxide from no-till and conventionally tilled farm soils. I was relieved to find that the emissions are no higher and often lower with no-till except on very poorly aerated soils. So it seems that earthworms are both part of the problem and part of the solution when it comes to climate change.
So if you find earthworms out in your garden or compost pile, don’t hurt them. They are probably still good on the whole.
Earthworm photo from schizoform. via Flickr under Creative Commons License