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Rolling's red flags
Amid the rush to roll, some Extension experts are raising a red flag about the practice.
“I’m very concerned about damage to soil quality,” says ISU’s Al-Kaisi. The big drums “crush soil aggregates” on the surface, he says, raising the risk of crusting, reducing water infiltration and increasing the potential for soil-surface compaction, surface runoff and wind and water erosion.
Despite the size of the big rollers, deep soil compaction isn't much of a concern, according to Mark Hanna, ISU Extension engineer. The drums exert a packing force of about 3 lbs./sq. in., he says, similar to the pressure exerted by the closing wheels of a planter.
“The jury is still out on this,” Hanna admits. “I understand that it’s frustrating if a rock goes up onto the grain platform or into the combine.” But, he adds, “I’m a little skeptical about whether it’s a good idea in the long run.”
Both Hanna and Al-Kaisi also question the payback for rolling.
“It’s hard to see how the cost is being recovered,” Hanna says. “I hear it reduces the amount of soybeans left in the field, but I’m skeptical of that. Earlier research shows that if the beans are standing well and the combine is well adjusted, stubble-cut loss is less than 1 bu./acre, and should be closer to half a bushel.”
Al-Kaisi points to “the additional time, fuel and machinery cost” of rolling. “Is this an economically sound practice,” he asks, “even allowing for downtime for machinery repair?”
He continues: “What is the problem being solved? There is a lot of good technology to adjust and calibrate the combine correctly” and manage residue. If you have rocks, he adds, “hire some kids to pick them up. It’s cheaper.”
Naeve counters: “You can’t find kids to pick rocks these days. And it’s the rocks the size of eggs, which we don’t pick up, that damage the sickles.”
Some fields are better suited for ground rolling, says Seth Naeve, a University of Minnesota Extension soybean agronomist (and a distant relative of Gary Naeve). Instead of “rubber stamping the practice for every soybean acre,” he recommends “a more prescriptive approach.”
For example, rolling is a good fit for higher-value seed beans or food beans, where dirty beans could be docked at the elevator, says Jodi DeJong-Hughes, an Extension tillage specialist who led ground-rolling trials at the University of Minnesota.
It also makes sense for flat, rocky fields, she says, although she points out that “eventually, you’re going to have to pick rocks. Rolling doesn’t push down anything bigger than a football-sized rock.”