Growers who switch to narrow-row soybean production may not need to spend more on seed. Research conducted at the University of Minnesota indicates that growers don't need to increase their seeding rate for narrower-row spacing. “We've determined through our research that farmers can use the same seeding rate irrespective of their row spacing from 7-in. to 30-in. rows,” says Seth Naeve, Minnesota soybean extension specialist. “This means farmers can switch to narrow-row systems without increasing their seeding cost.” The Minnesota research conducted over four years and across 19 environments found that the optimum seeding rate was the same in 10-, 20- and 30-in. rows at each location studied. The optimum seeding rate does vary by maturity zone, however.
For 2003, the University of Minnesota recommends a single seeding rate of 170,000 seeds/acre for Group 2 soybeans in southern Minnesota. This is a change from earlier recommendations of 160,000 seeds/acre for wide rows and 180,000 seeds/acre for drilled soybeans. As you move north, the optimum seeding rate increases. In northern Minnesota, the seeding rate recommendation for group 00 soybeans is 200,000 seeds/acre.
Most other states still recommend higher seeding rates as row spacing narrows, but most think a number of farmers could benefit from fine-tuning their seeding rates, especially with the increased use of more expensive Roundup Ready seed.
How much is too much?
Research in Ohio has shown that maximum profits for Roundup Ready soybeans occur at seeding rates of 160,000 to 190,000 seeds/acre in 7- to 17-in. rows in productive environments. “There are a number of farmers who are planting 200,000 to 250,000 seeds/acre when they are drilling soybeans. Those rates are much higher than they need to be,” says Jim Beuerlein, Ohio soybean extension specialist.
Ellsworth Christmas, Purdue University extension agronomist, agrees. “Many farmers plant 225,000 to 250,000 seeds/acre, and there's no reason to do that,” he claims. “It's just wasted money.”
Indiana's seeding rate recommendations are 200,000 seeds/acre for drilled beans, 165,000 seeds/acre for 15-in. rows, and 130,000 seeds/acre for 30-in. rows. Christmas notes that farmers with precision planting equipment and high-quality seed can reduce these rates by 10% and still end up with a good stand. He does caution that a lower planting rate may not offer canopy closure as early and may require a second application of Roundup.
Stand evaluations in Minnesota show there is room for improvement in planting rates. “Minnesota Department of Ag field surveys show that 24% of the fields in Minnesota have super-optimal soybean stands, but another 26% have deficient stands,” Naeve reports. “Only half of the fields end up with an optimal final plant stand between 125,000 to 175,000 plants/acre.”
Widen your harvest window
As growers try to plant and harvest more acres with the same equipment, they are pushing soybean planting earlier and earlier. “I'm concerned about farmers planting soybeans too early and subjecting them to undo stress for a month for no good reason,” says Ellsworth Christmas, Indiana extension agronomist. “Soybeans planted on April 10th won't flower any earlier than soybeans planted on May 10th.” He offers another strategy to spread fixed machinery costs over more acres, and that is to plant earlier maturity soybeans.
“If you normally plant Group 3.5 soybeans, consider planting a portion of your acreage to Group 2.5 or 2.0 soybeans,” Christmas says. “If you plant the earlier maturity variety first, it will mature first and that will widen your harvest window and allow you to spread combine costs over more acres.”