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Serving: IN
combine unloading soybeans into wagon in field
WEIGH AND COMPARE: Jim Zimmerman completed four years of replicated testing of soybean seeding rates on his farm in Jay County, Ind., last fall.

On-farm trials reveal lessons about soybean seeding rates

A four-year trial tells this farmer he can cut back, except if he must plant very late.

What’s the best way to know if you can cut soybean seeding rates? Jim Zimmerman, Redkey, Ind., believes it’s conducting testing on his own farm.

“I was seeding around 210,000 seeds per acre and didn’t think I needed to be that high,” Zimmerman says. His soybeans are in 15-inch split rows.

To find out where he should be, he agreed to work with Larry Temple, then the Jay County Extension educator, to set up a replicated trial to see what he could learn. That was in 2016. Four years later, Zimmerman is confident in cutting back on seeding rates. How much he cuts back depends upon when he can plant and what he feels comfortable with doing. He’s now more comfortable planting 140,000 to 160,000 seeds per acre.

Temple retired as Extension educator in September, but he returned to help Zimmerman complete harvest of his replicated soybean seeding rate trial last fall. Temple notes that as the trial progressed over time, he suggested a few changes, based on what they learned and what Zimmerman intended to do in the future.

What results show

“We dropped the 210,000 seeding rate,” Temple says. “Then in 2019, we added an 80,000 seeding rate just to see what would happen. Shaun Casteel at Purdue, the soybean specialist, continues to show surprising results for seeding rates which most people consider too low.”

After four years, Temple reached two conclusions. “First, the results from 2016 through 2018 showed no significant difference in yields for seeding rates,” he says. “That includes seeding rates all the way from 100,000 to 210,000 seeds per acre.”

soybean seeding rate trial chart

Temple acknowledges that there’s a difference in seeding rate and harvest population. He suggests keeping that in mind when settling on 2020 seeding rates. In 2019, actual harvest populations in Zimmerman’s trial varied from just under 85% to over 90% of seeding rate, depending upon population. See the table above for exact harvest populations.

“Second, results in 2019 indicated that when planting late, a higher seeding rate is definitely the correct practice,” Temple concludes. The trial was planted in late June. The 190,000 seeding rate yielded best in 2019, although 100,000 seeds per acre ranked second. The 80,000 seeding rate, with 67,000 actual plants, was third.  

TAGS: Planting
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