Mar 12, 2017
As I expected, my commentary from the field prompted sharp responses such as this one from Kent Stones:
"You stated that for the last ten years you have subscribed to the theory of man influenced global warming. My question is if this is settled science in your view, why would you not be contributing to the solution by adopting a lower carbon dioxide emitting cultural practice on your own farm i.e. no-till. Or is the solution someone else's problem?"
Thanks for the question, Kent and send me an address for your mug. I thought I knew the answer to your question but my research surprised me. Let's deal just with the carbon sequestration issue today. The best information I could find was from a 2014 study at the University of Illinois. It was a meta-study, or a compilation of all available work to date.
The conclusion was that while no-till may increase the soil-organic carbon (SOC) in the top few inches, the lower layers are a different story.
The summary by lead soil scientist Ken Olson was:
"The subsurface layers also need to be sampled and tested to the depth of rooting, or 1 or 2 meters. That no-till subsurface layer is often losing more soil organic carbon stock over time than is gained in the surface layer."
One important note is Olson stresses using cover crops could improve sequestration, but much more research needs to be done on that factor.
To be sure, conventional tillage was not better, but wasn't much worse either. In fact, the most generous sequestration claim I found for no-till is under one ton per acre.
Actual field fuel use is much less. We average about 4 gallons of diesel per acre per year. No-till might cut this in half, dropping emissions by about 40 pounds per acre. This is not trivial, but it is not the whole answer either. Even if all the cropland in the US could sequester 1 ton per acre, our sector, which generates 9% of emissions, would approach zero net emissions.
Larger reductions can be made faster by decreasing fossil fuel-electricity use with solar power, for example, or driving higher mileage vehicles.
I will talk about greenhouse gas accounting another time, but the short version is the decision to no-till can be made for many reasons. Carbon sequestration does not appear to be one of the most important.