Optimum Planting Rate Revealed
Published: Friday, January 31, 2025
Michigan State University Extension soybean educator Eric Anderson gave an update on soybean research to Southwest Michigan farmers last Tuesday in Three Rivers.
Dozens of farmers gathered at GreenMark Equipment to hear the soybean research summary and updates, which included over a dozen on-farm trials.
Anderson discussed many different studies, including: planting timelines and maturity, seeding rates, spring tillage effects on yield, white mold fungicide application timing and the effect of potash on yield.
Planting dates were studied across three locations in Branch, Kalamazoo and Shiawassee counties. The trial focused on two variables, planting date and maturity group. The Kalamazoo and Branch county locations focused on planting dates, with early dates of two maturity groups at April 22 and 25 and later planting dates at May 17 and 19, respectively. The Shiawassee field planted two maturity groups on only May 2.
"In Kalamazoo, the longer (season) bean was different, but in Branch, there was no difference between maturity group," Anderson said.
Yields in Kalamazoo were 74.5 bushels per acre in for the early planting of the shorter maturity group, compared to 68.4 bushels per acre for a later planting date. Also, the longer maturity group yielded 77.2 bushels per acre in early planting and 67.5 bushels per acre.
In Branch, yields were 54.9 bushels per acre in the early planted short maturity group and 39.7 bushels per acre in the late planting. Long maturity yields (bu./ per acre) were 58.3 in the early planting and 44.1 in the late planting.
With only one planting date, the Shiawassee location yielded 74.8 bushels per acre in the short maturity group and 71.1 bushels per acre in the longer maturity group.
Overall average income for early planting, shorter maturity group; early planting, longer maturity group; later planting, shorter maturity group; and later planting, longer maturity group were: $735, $744, $607 and $626, respectively.
To find the optimum planting rate, participating farmers planted at set rates of 70,000, 100,000, 130,000 and 160,000 seeds per acre.
"Agronomically, the yield itself continues to rise with the higher planting rates," he said.
However, the results showed that the economically best rate was 100,000 seeds per acre.
A third on-farm trial focused on spring tillage effects on soybean emergence.
"Does it improve yield?" Anderson asked.
The cost per tillage pass was $14 per acre.
"For the most part, there was not a lot of difference," he said. "The overall average difference was 1.4."
The average income of tilled and no-tilled land were $529 and $528, respectively.
"There is a statistical difference between the tilled and non-till," Anderson said. "More plant stands were reported with tilled than no-till fields."
The difference was (no-till vs. tilled):
• Cass County (Mich.): 107,000 versus 108,200;
• Branch County: 60,887 versus 66,647
• Ottawa County 20: 81,200 versus 80,400;
• Ottawa County 21: 88,300 versus 91,200
The average stand difference across all nine fields was 5,406.
A two-year trial to determine the impact of fungicide application timing was conducted from 2023-24. Fungicide applications occurred at R1, seven days after R1 and 14 days after R1. However, no yield differences were detected among the treatments at any location in 2024. The only difference for 2023 was found in Sanilac County, where yields reached 6.7 in field strips treated seven days after R1 and 6.3 14 days after. This is a difference of 2.4 and 2 from the control (4.3 bushels per acre difference), respectively.
Only one of three locations, a farm in Allegan County, yielded data concerning the potassium fertilizer trial, showing the effects of muriate of potash (potash) and sulfate of potash (SOP). One thing Anderson and other researchers found was that many farmers were especially interested in low-salt level potash.
"They were more interested in a form of potash, Anderson said. "They'd heard that the high salt in the potash was maybe causing some emergence issues, causing some stunting and affecting yield," he said.
The purpose of this trial was to determine whether soybean yield and net income are affected by potassium fertilizer sources.
"2024 was the first year we've run this," he said.
The potash variations were applied on June at a rate of 150 pounds. The ground was chisel plowed with a high-speed disc. The planting date was June 12 and there were .9 inches of rain between the potash application and planting.
"If you get that on a few weeks ahead of time, you're probably safe. So, here, we're only looking at about a week and a half and about an inch of rain. Anecdotally, I've heard from other educators that they've told folks over the years that if you get an inch of rain, you're probably safe," Anderson said.
The soil test showed soil pH of 5.4, with 14 parts per million phosphorus, 68 ppm potassium, 63 ppm manganese and 421 ppm calcium.
The effects showed potash yielded 40.4 bushels per acre and SOP yielded 40.1 bushels per acre. The net income for each was $394 and $372, respectively.
"We are going to run that one again," Anderson said about the experiment. He invited farmers who are interested to join in the trials.
Other discussed trials were: soybean seed inoculation, in-furrow starter fertilizer, in-furrow Radiate and Accomplish Max, ILeVO vs. Saltro seed treatment, ArchiTech plant growth regulator/foliar fertilizer, Delaro Complete foliar fungicide for high yield, Delaro Complete foliar fungicide for white mold, and slug damage in soybeans.
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