When rolling emerged soybeans timing is important, says Dennis Lange, pulse crop specialist with Manitoba Agriculture.
Conditions need to be right to avoid crop damage. Soybeans shouldn’t be too young or too old and the air temperature should be at least 25 C and ideally closer to 28 C.
Rolling, which is done to flatten the field to make harvesting easier in the fall, shouldn’t begin until plants are at least at the first trifoliate stage.
“The reason you go at the first trifoliate is you want to make sure all the beans are passed the hook stage (when they are more susceptible to breaking when rolled),” Lange said in a soybean field June 15.
When soybeans first emerge the cotyledons are visible followed by a unifoliate (two true leaves — one each side of the stem). Next is the first trifoliate stage when three leaves emerge as a leaflet. Rolling can continue in the early two trifoliate stage, but farmers should roll a short strip and assess the damage before rolling the whole field, which applies when rolling at any stage, Lange said.
“Typically for a 22-inch row (spacing) you measure off 23 feet, nine inches and count off the number of plants in that distance to determine (plant) population and along with that you want to count the damaged plants to determine what you are actually losing,” he said. “So long as you are in that 140,000 to 160,000 plants (per acre) that emerge and are not damaged then you are in the money as far as (potential) yield goes.”
The Manitoba Pulse & Soybean Growers (MPSG) says 140,000 to 160,000 soybean plants per acre is equivalent to 3.2 to 3.7 plants per square foot, 35 to 40 per square metre and 14 to 16 within a 28.4-diameter Hula Hoop.
Sometimes broken soybean plants will regrow, depending where the stem breaks, Lange said.
The weather should be warm when rolling soybeans.
“If it’s at least 25 C when you start rolling, and ideally, a little bit warmer is better,” he said. “You want to be rolling in the afternoon. Even if you have a warm morning you are better off waiting until the afternoon when the plants are very pliable and making sure they are at the right stage. The first trifoliate is ideal.
“The biggest reason you want to roll is to make your harvest field much easier to work with. To me the biggest reason you want to roll is if you have stones. If you have stones in the field you want to push them down in the soil to anchor them in so they aren’t going to come up into the combine later on.”
The best time to roll soybeans is “immediately after planting or within two days of planting,” says the May 31 edition of the MPSG’s Bean Report, but not if the field is wet. Rolling then can pack the field resulting in a crust on top making it hard for seedlings to emerge.
Rolling dry soils before seedling emergence can leave soil powdery and vulnerable to wind and water erosion, the MPSG Bean Report said.