Walking around the exhibits at Farmfest last week, I had a "Wait, what?" moment.

Amid its usual collection of giant John Deere combines and tractors, farm dealer Kibble Equipment had an ordinary plow with an extraordinary sign: "The Last Plow Sold By John Deere."

Wait. What?

John Deere — the man — in 1837 invented the steel plow that opened the American prairie to the pioneers. He put his company next to the first railroad bridge across the Mississippi so that settlers heading west could buy a plow from him on their way. The Smithsonian included an 1838 plow by Deere in its "101 Objects that Made America" exhibit.

Minnesota's soon-to-be-replaced state flag depicts a farmer with a plow. "We could start agriculture" because of it, said Jodi DeJong-Hughes, tillage expert for the University of Minnesota Extension.

But last year, Deere & Co. announced it would halt production of its 3710 moldboard plow, the one that most resembled the original design of its founder.

It's a decision born of a market reality. Farming has changed. The U.S. Department of Agriculture last year reported that a majority of U.S. farmers use no-till practices, with disks or chisel plows that create a narrow furrow rather than turning over land as a moldboard plow does. A moldboard is a curved metal plate.

Deere still has a reversible plow on the market, which has a different moldboard than the 3710. The company also has a full catalog of cultivators, rippers and other tillage equipment.

Since the Dust Bowl era of the 1930s, critics blamed the moldboard plow for contributing to topsoil erosion. Soil scientists and environmentalists for decades urged farmers to adopt planting practices that were less disruptive.

But there are many other reasons for the declining use of the plow.

Here in the Midwest, for instance, DeJong-Hughes noted there's far less growth of alfalfa and other perennial grasses that are best cultivated with plows. Decades ago, herbicides came along, replacing the plowing over of land as the best weapon against weeds.

And then, crop planters got better, making it possible for seeds to be deposited in the smaller furrows. Combines, which throw off chaff at harvest, changed to distribute those leftovers more widely so that the ground didn't need to be churned up for planting the next spring. New hybrids of corn and soybeans emerged that grew better through the residue of last year's plants.

Then in the 1990s, the USDA stepped in with environmental quality incentives that encouraged farmers to adopt low- or no-till soil management. Farmers started to be OK with residue left between rows of plants, an important change in psyche.

"It wasn't that long ago that if a farmer didn't till his soil black, totally black, he wasn't considered a good farmer," DeJong-Hughes said.

It all adds up to the moment Deere & Co. found itself ready to let go of the product that gave the company its start. The company has said little about it. And it doesn't mean much financially: Deere gets far more revenue and profits from tractors, combines and other big equipment.

And yet, the evolution of the plow and John Deere's role in it is as exciting and full of entrepreneurial verve as any more modern tale about cars or TVs or smartphones. Ancient Chinese, Greek and Egyptian civilizations all created versions of plows pulled by animals, essentially sticks that opened the ground.

The Romans are credited with creating the first iron plowshare, and the Dutch and Scots made other improvements. A German poet penned "We Plough the Fields and Scatter" in 1782, and the words were set to music in 1800 as a hymn that's still sung in churches today.

But it was in America in the late 18th and early 19th centuries when a true race to create the best plow began.

Deere, a blacksmith in Grand Detour, Ill., wasn't the first to use steel but his plow in 1837 was the first to self-scour, which meant that farmers no longer had to stop every few feet to clean the plow blade.

By 1860, there were 2,000 companies in the U.S. making plows. Deere by then had moved to Moline, Ill., where the railroad crossed the Mississippi. "He had folks stopping and buying plows on their way west," Neil Dahlstrom, an archivist at Deere & Co., told me.

In 1869, the company opened its first branch sales office in Kansas City and soon had a network of offices along the rivers of the Midwest, including in the Twin Cities.

The next decade, Deere began selling sulky plows that farmers could ride on instead of walk behind. That innovation was driven by demand after the Civil War, when many veterans returned to farms with injuries, Dahlstrom said.

By the 1880s, it was selling steam engines that could pull plows. The company's first tractor went on sale in 1918.

"The underlying theme is how can you continue to do more," Dahlstrom said. "But the basic design of the plow doesn't change a lot."

In America's fields, everything else did.