By Nathan Mueller, Jenny Rees and Laura Thompson

Nebraska Extension has a long history of working with farmers to conduct on-farm research, especially on soybean seeding rates. In 1989, 20 Saunders County producers came together through Extension to form the Nebraska Soybean and Feed Grains Profitability Project.

This group began doing randomized, replicated research to answer questions that affected the profitability of their farming operations.

In 1990, the first seeding rate study evaluated 150,000 seeds per acre compared to 225,000 seeds per acre in Saunders County. What did the first study find? The lower seeding rate yielded 53 bushels per acre, while the higher seeding rate yielded 52 bushels per acre — not a statistically significant yield difference.

Because of the original group's success, the idea spread to surrounding counties, and in 1998, the Quad Counties research group formed in Clay, Fillmore, Hamilton and York counties in south-central Nebraska.

Extension educators and specialists worked with 20 farmers to produce reliable, unbiased research. The Nebraska On-Farm Research Network builds upon the success of these two organizations, expanding on-farm research to a statewide effort in 2012.

Years of data

Twenty-five soybean seeding rate studies were conducted between 1990 and 2018, including some studies performed under 15-inch and 30-inch row spacing — and on nonirrigated and irrigated fields. You can find and view past (2018 and earlier) soybean seeding rate studies conducted by Nebraska farmers online at resultsfinder.unl.edu.

Over the past six growing seasons, results from 10 studies that used similar seeding rates of 90,000; 120,000; 150,000; and 180,000 per acre found a yield increase of 2 bushels per acre by increasing the seeding rates from 90,000 to 120,000 — with no further yield increases above 120,000 seeds per acre.

In 2018, three soybean seeding rate studies also showed no advantage to increasing seeding rates above 100,000 seeds per acre in two studies and 120,000 seeds per acre in the other.

In 2019, Nebraska producers conducted 11 additional studies that were shared at on-farm research results meetings across the state in late February. Six studies were part of a data-intensive farm management project where four seeding rates were evaluated at 80,000; 110,000; 140,000; and 170,000 per acre.

Rather than using field length replicated and randomized strips, these studies relied on using precision ag technologies such as variable-rate seeding capabilities and in-cab monitors to implement numerous small blocks of seeding rates in various portions of the field. There was no significant yield increase with seeding rates higher than 110,000 seeds per acre.

There were five other 2019 studies, and no additional yield increases were realized with seeding rates higher than 120,000 seeds per acre, except at one site where hail occurred. At the site with hail damage, 150,000 seeds per acre did yield higher than 100,000 seeds per acre.

With 36 studies under its belt now, the Nebraska On-Farm Research Network has shown that a seeding rate of 120,000 seeds per acre has performed well across counties, farms and fields in Nebraska.

Figure 1. Location by county for soybean seeding rate studies through the Nebraska On-Farm Research Network from 1990 to 2019. 

Current recommendations from Iowa State University are 125,000 to 140,000 seeds per acre. Current recommendations from Kansas State University are dependent on the yield environment and achieving target final stands or plants per acres.

Kansas State University results show 127,000 plants per acre in low-yield environments and about 100,000 plants per acre in a medium- or high-yield environment maximizes yield. Regional research data has concluded that 100,000 plants per acre at harvest is a great target.

Things to consider

Is a planting rate of 120,000 seeds per acre always going to be enough? In some situations, you may consider higher seeding rates when you have a lower-than-normal germination percentage on the seed lot, fields with history of stand establishment issues such as seedling diseases and crusting, or fields with a history of iron deficiency chlorosis.

Additionally, if you have variable-seeding-rate capabilities, some research studies have shown a slightly higher rate may be a benefit in low-yielding areas. Some try to minimize the risk of a poor stand through using fungicide seed treatments, planting extra seeds per acre and buying hail insurance.

Is fungicide-treated seed planted at 180,000 seeds per acre and buying hail insurance too costly a risk management plan? Afraid of planting 120,000 seeds per acre? Try this: Buy hail insurance, use fungicide-treated seed, but reduce your seeding rate down to at least 140,000 seeds per acre, which is one unit or bag per acre.

If you don’t want to bet the farm on it, conduct your own on-farm research. Learn more about the Nebraska On-Farm Research Network at cropwatch.unl.edu/on-farm-research or contact your local cropping systems educator through your Extension office.

Mueller is a Nebraska Extension cropping systems educator; Rees is a Nebraska Extension cropping systems educator; and Thompson is a Nebraska Extension On-Farm Research Network coordinator.