When is the best time to roll soybeans?

That’s one of the main questions farmers are asking about this new practice, says John Holmes, Iowa State University (ISU) Extension field agronomist. Recent research in North Dakota, Minnesota and Iowa evaluated the timing and risks of rolling soybeans.

University of Minnesota field-scale trials in 2009 and 2010 looked at rolling immediately before and after planting, at cracking and at V-1 and V-3. The research found that rolling did not significantly affect stand counts or yields, says Jodi DeJong-Hughes, a University of Minnesota Extension tillage specialist.

“We did all of our rolling in the afternoon when the plants were a little limp to decrease injury,” she notes. Rolling at V-3 did cause more plant damage, she says, but that damage didn’t lower yields. “Wheel traffic caused more damage than the actual rolling.” Still, she adds, “You are definitely increasing your risks if you roll after the plants are up,” so it’s safest to roll just before or after planting.

The Minnesota research also found that “rolling raises the risk of sealing the soil and consequent ponding,” DeJong-Hughes says. Leaving more residue on the surface protects both the soil and the plants from the roller, she adds. However, blowing residue can be an issue after rolling. Wet soil or cool, cloudy conditions also raise the risk of plant damage from rolling, she says.

Rolling may intensify runoff, too, especially on sloping fields. Trials in northern Iowa in 2010 showed that rolling “cut water infiltration rates by about 150%,” says Mahdi Al-Kaisi, an Iowa State University Extension soil scientist. “It’s only one year of data, but it raises questions.”

The Minnesota and Iowa findings confirm earlier research by North Dakota State University (NDSU). Trials in 2003 and 2004 concluded that “there was no yield loss from rolling,” says Greg Endres, an Extension soil scientist at the Carrington Research Extension Center. “But injury levels go up if you delay rolling until the first trifoliate stage,” when plants are 3-4 in. tall. “If you roll after the crop emerges, we recommend doing it at the unifoliate stage because the plant can recover more easily.”

NDSU also found that rolling breaks down soil-surface aggregates, increasing the potential for crusting and erosion, especially in finer-textured soils, Endres says. “If we have strong winds after rolling, that thin layer of soil can blow, or if we have heavy rains, it can wash.”

Judd Moore is an agronomist for New Horizons Ag Services in Chokio, MN. The co-op has been custom rolling soybean ground in west-central Minnesota for seven years, and keeps three 50-ft. Degelman rollers busy every spring. “We have been able to roll up to V-3 as long as the stems are soft” and the ground and plants are dry, Moore says. “You can’t roll if there is dew, because the plants stick to the rollers.”