A man locally here is obviously proud of his tillage equipment and takes very good care of it mechanically. It’s always clean and parked near his home by the highway as a public testament to the pride he has in the tools he uses to farm his northern Oklahoma fields.
I’ve never met this man, but I surmise he is known in the coffee shop as a “good farmer,” and I’d bet he’s probably paying his annual bills with his wheat, soybean and sorghum crops.
I never drive by his place, however, without remembering several years when heavy autumn rains hit his neatly-tilled, bare hillside wheat field and deposited tons of upland soil into an “alluvial plain” at the bottom near a bordering county road.
That, too, was a testament of conventional farming the fragile soils of Oklahoma – in plain sight for all to see who drive that busy highway. I privately ponder how that affected his overall bottom line after he waited for the field to dry and re-tilled everything to late-plant $3 wheat.
Recent studies show erosion is moving a ton of topsoil per acre per year across all classes of farmland in the U.S. In the Midwest, where native tall grass prairie was converted to agriculture in the mid -1800s, researchers estimate more than 57 billion tons of topsoil has eroded.
Isaac Larsen, a geologist at the University of Massachusetts, has used remote sensing to measure the differences in elevation of remaining patches of native tall grass prairie and adjacent cropland. In a 9-state study at 20 sites, the researchers measured 10 or more spots per site and, on average, found cropland fields were nearly 15 inches lower than prairie soils. That soil went somewhere.
This corresponds to the loss of roughly 1.9 millimeters of soil per year from agricultural fields since the estimated start of traditional farming at these sites more than a century and a half ago. That rate is nearly double the maximum of one millimeter per year that the USDA considers sustainable for these locations, and quadruples widely-used estimates of 0.5 mm of average annual farm soil loss.
Popular models estimate, under natural conditions, a millimeter of soil takes more than 25 years to form, whereas the annual erosion of farmland is estimated to be 0.5 millimeters. So erosion is about 25 times faster than soil formation.
USDA currently estimates the erosion rate in the Midwest in two ways. One way estimates the rate to be about one-third of that reported by the researchers. The other estimates the rate to be just one-eighth of the researchers’ estimates. Those USDA estimates do not include tillage.
Studies show the obvious: Disrupting the soil structure by plowing increases water runoff and erosion due to soil moving downslope.
Larsen says the effects of tillage should be incorporated into the USDA’s erosion estimates. Then the USDA numbers might better align with the 57.6 billion metric tons of soil that the researchers estimate has been lost across the Midwest in the last 160 years.
If they need a sterling example, I know where they can find it.
