April 4, 2008 

More not Always Better

In two years of on-farm, replicated research, several Nebraska soybean producers found little or no yield benefit from planting more than 150,000 seed/ac.

"The results were surprising," said Dan Aspegren, a corn and soybean producer who conducted one of the trials on his farm near Geneva. His seed company had been recommending higher and higher seeding rates. "They do a lot of research on their own," Aspegren said, and he had always felt comfortable following their recommendations. "The trend is 'More is better', but we didn't find that to be the case here."

Replicated trials in 2006 and 2007 looked at initial planting rate, final populations and yield at farms in Fillmore, Seward, Nuckolls, Hamilton, Clay and York counties. Each study was replicated at least three times at each location. The research was conducted as part of the Quad County On Farm Research Group (see story), a collaborative project of producers and UNL Extension.

Previously, Aspegren had been planting about 165,000 seeds per acre, but has now dropped the rate to 150,000 to 155,000 seeds per acre.

Like Aspegren, Brandon Hunnicutt, another researcher in the Quad County Group, has dropped his seeding rate for soybean. He expects to plant 140,000 to 150,000 seeds/per acre this year. Hunnicutt, who at one time planted 180,000-200,000 seeds per acre, said he had been dropping the rate prior to participating in the study, but after seeing the results, he's dropping the rate further.

"The research confirmed that we can maintain yields with lower populations, and even more interesting is that we could without it being detrimental to yield or economic yield," Hunnicutt said.

Trial Results

In trials in five irrigated, ridge-tilled fields in 2007, yields ranged from 59.4 bu/ac (90,000 seeds/ac) to 60.2 bu/acre (180,000 seeds/ac). This represented a 1% increase in yield for a 100% increase in seeding rate.

In 2006 yields in two irrigated trials ranged from 65.5 bu/ac (90,000 seeds/ac) to 67.4 bu/ac (180,000 seeds/ac). This represented a 3% increase in yield for a 100% increase in seeding rate. In the one dryland trial, yields ranged from 38.7 bu/ac (100,000 seeds/ac) to 42.7 bu/ac (160,000 seeds/ac), a 10% increase in yield for a 60% increase in seeding rate. However, this field received hail at the cotyledon stage and was not replanted since it was dryland. Final stands resulted in plant populations as low as 67,000 plants/acre (for the 100,000 seed/ac planted rate) and 102,000 plants/acre (for the 160,000 seed/ac planted rate).

"The yield in this particular field was amazing considering the very low plant populations after the hail. August rains helped this field in 2006," said Jenny Rees, another Extension Educator working on the project.

Economic Advantage

This places a pretty high seed cost on what was less than a bushel per acre increase in 2007, said Gary Zoubek, one of the Extension educators working with the Quad County Group to design the research. While this research represents only two years, the results were generally consistent from site to site and from year to year, he said. In 2007 there was no significant difference in soybean yields in plots planted at 90,000, 120,000, 150,000 and 180,000 seeds per acre, he said. Farmers selected the seed and practices they used.

Reducing the seeding rate by 40,000 seeds/acre would result in an average savings of $9/ac. Total savings for the Clay, Fillmore, Hamilton and York county area containing 270,000 soybean acres in 2007 would have been $2.5 million, Rees said.

Other Plant Population Effects

The research also showed that plant population affected the number of pods per plant. As the plant population increased, the number of pods per plant decreased. Planting date did not appear to have an interaction with plant population at any of the 2007 sites, with planting dates ranging from May 4 to June 4.

Planting rate did appear to contribute to a difference in plant stalk strength. About a month before harvest Aspegren's trials received almost seven inches of rain in 1.25 hours. In the high population plots, the beans were laid over and flat to the ground. In the lower population plots, the plants were standing and appeared to have stronger stems to withstand the pounding rain better. While this wasn't part of the statistical research, it certainly made a visual impression about the benefits of lower populations, Aspegren said.

Researchers

Producers participating in the 2006 Soybean Population Study were Aspegren, David and Doug Cast of Beaver Crossing, Rick Hughes of Geneva, and John Dolincek of Lawrence. Producers participating in the 2007 Soybean Population Study were Aspegren, the Casts, Jerry Stahr of York, Don and Mike Campbell, Aurora; Brandon and Daryl Hunnicutt of Giltner, and Alan and Kevin Songster of Exeter and Beatrice, respectively. Another test site was located at the South Central Ag Lab near Clay Center.

Extension educators contributing to the study were Zoubek, York County; Rees, Clay County; Brandy VanDeWalle, Fillmore County, and Jim Schneider, Hamilton County.

For more information on the Quad County On Farm Research Group and other on-farm research opportunities offered by UNL Extension, visit UNL's On Farm Research Web site, call one of the participating Extension educators, and see the story in this week's CropWatch.

Lisa Jasa
CropWatch Editor