By Dan Towery
FROM THE WEB EDITOR: In response to the focus on alternative energy as the great salvation against excess CO2 in the atmosphere there was a recent piece written on the Ecowatch website: https://ecowatch.com/2015/11/18/soil-oceans-paris-cop21/. The following is Dan Towery’s response to that post.
Agriculture crop fields have lost significant amounts of organic matter (carbon) via soil erosion and tillage (30-50% of total organic matter). Pasture and rangeland which has been overgrazed has also lost significant amounts of organic matter.
There are 2 basic types of organic matter. Passive organic matter is centuries old and is very stable (Prairie soils). This portion of the OM is only lost through soil erosion and ends up in sediment. Whereas, the active organic matter portion is relatively new (2-5 years old) and the carbon is lost through tillage operations. This carbon is released into the atmosphere as CO2 and is the result of oxygen being stirred into the soil.
Planting cover crops and minimizing tillage (no-till) will add active organic matter to the soil. However, this organic matter is also very fragile. Most of the active carbon is in the top 2″ of the soil. 5 to 10 years of accumulated active carbon can make the soil more resilient and provide nutrients to following crops. However, this carbon can be lost if management changes, i.e. Cover crops not planted or multiple full width tillage trips occur. What took 5-10 years to gain can be lost in 1-2 years.
So while crop fields have the potential to be an incredible carbon sink, the needed management isn’t there on many acres at this time. In the US cropland managed to sequester C is somewhere between 10-15% of all cropland acres. However, the number of acres is increasing. But this carbon could also be released into the atmosphere if management changes, i.e. the farm changes hands (owner or tenant). This carbon is very important but is also very fragile.
Grazing lands can also increase the active carbon if planned grazing is utilized. Whereas, overgrazing will result in a loss of active carbon in the soil.
Working with farmers in the Midwest to adopt no-till and cover crops is what I do. Change is slow both in the rate and acres involved with increasing the active carbon in the soil. And a management mistake can cost yield and lower profits for the farmer.
Dan Towery has operated Ag Conservation Solutions as a Midwest conservation agronomist over 10 years. But has spent over 30 years working on improving soil health. dan(AT)agconservationsolutions(DOT)com