Strange sights are appearing each spring on more and more Minnesota seed fields. You’re seeing huge rolling drums pulled by huge tractors. Stretch your imagination to a 40-foot wide rolling pin smoothing out baking dough on a 160-acre bread board.

Farmers simply call it “ground rolling.” According to Jodi DeJong-Hughes, University of Minnesota Extension educator specializing in crops at Marshall, it’s “catching on like wild fire. It started in northwest Minnesota mainly to push down rocks so combine operators could set the header to ground level to cut even the lowest pods, without catching a rock.”

Now ground rolling is spreading throughout Minnesota, according to DeJong-Hughes. A key benefit is reduced stress: combine operators are more relaxed when running their rigs across fields that have been rolled.

Rocky options

Working your combine through a soybean field littered with small rocks likely results in two possibilities, neither desirable: 1) raise the header to skip over the rocks and leave three to four bushels per acre, or 2) go for those low-hanging pods and possibly run a few rocks into your machine. Rock collectors in most combines catch most rocks before they get into the threshing cylinders, but they don’t catch all rocks, and there’s the rub.

Improved harvest ability is the obvious payoff to rolling your seed beds, DeJong-Hughes said, and there may be other economic advantages. But one key question persists: when is the best time, before planting or after?

“We’re setting up timing trials this spring, both pre-plant and post-planting,” DeJong-Hughes said. “Some suggest roll just ahead of the planter. Others suggest just after planting for better seed-to-soil contact. Also we’ll be looking at soil moisture. Are there risks if soil is too wet? Could you have compaction so emergence is affected? Do we end up with better stand count because of rolling? Is surface erosion minimized with rolling? Or could erosion be even more a factor?” She and research assistants Doug Holen and Phil Glogoza are exploring these questions.

Reporting on three plots that were rolled last spring, she said there was no improvement in emergence and no difference in final stand count between rolled and unrolled plots.

Before or after planting?

DeJong-Hughes said most farmers roll their fields after planting simply because planting is a first priority. But she also noted some farmers roll before planting to break up root balls and prepare a smoother planting surface. By the same token, farmers who drill or narrow row their soybeans, then come in with the ground roller might just be messing up their seed bed. If zero-till or strip tillage is being done, corn stalks and root balls may decompose faster when the soil is rolled because more soil microbes can then start feeding on the residue.

Trials this spring will also help determine how long after planting before you ground roll. She indicated V3 growth stages will be rolled and some farmers have rolled even when soybeans were already measuring one foot of growth.

“I wouldn’t recommend that,” she said, “but depending upon circumstances of time and weather, maybe rolling your seed bed can be done later than would seem logical. It might even depend on the soybean variety. Lots of questions to things we just don’t know.”

Reduced erosion

Reduced erosion issue from rolling apparently is real. One of her plots this past spring did experience a significant rain storm shortly after planting. “We could see right to the row where we had rolled. It sealed the soil so the water didn’t infiltrate and plants drowned.”

Rolling machines range from 30 feet to 60 feet. Various brands are available. A 42-foot roller costs about $30,000. Iowa State University custom rates state that rolling costs about $8.50 an acre. If a farmer rents a unit to do his own rolling, cost is $3 to $4 per acre.

Are university agronomists and Extension educators ready to endorse ground rolling? “The logical answer is that we need more research,” DeJong-Hughes chuckled, “but I am hearing from seed houses and elevators that take in seed beans that beans from rolled fields are coming in cleaner. So if you’re a seed grower and don’t want to get docked for dirt with your beans, rolling appears to be the answer.”

Reality, however, is winning the minds of more Minnesota farmers. They don’t necessarily need more yield, or better stands, or less erosion. They simply tell DeJong-Hughes, “I’m going to roll. Better harvest ability is what this is all about. Eliminate the hazards of rocks and getting all my beans makes this a no-brainer.”

You can reach Jodi DeJong-Hughes at dejon003@umn.edu or (888) 241-3261.