Soybean Seeding Rate On-Farm Research

Location by county for soybean seeding rate studies
Figure 1. Location by county (shown by red fill) for soybean seeding rate studies through the Nebraska On-Farm Research Network from 1990 to 2019 based on the resultsfinder.unl.edu database. Counties with studies not currently in the database are noted by red lines and have been reported in CropWatch articles.

Soybean Seeding Rate On-Farm Research

Key Point: 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.

Nebraska On-Farm Research History

Nebraska Extension has a long history of working with farmers to conduct on-farm research, especially on soybean seeding rates. In 1989, twenty Saunders County producers came together through Nebraska 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 operation. 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.

Due to 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.

Soybean Seeding Rate Results

Between 1990 and 2018, 25 soybean seeding rates studies were conducted, including some studies performed under 15-inch and 30-inch row spacing and on non-irrigated 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, 120, 150, and 180K seeds per acre found a yield increase of 2 bushel 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 2 studies and above 120,000 seeds per acre in the other study.

Nebraska producers in 2019 conducted 11 additional studies that were shared at on-farm research results meetings across Nebraska in late February. Six studies were part of a data-intensive farm management project where four seeding rates were evaluated at 80, 110, 140, 170K seeds 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. This type of study can allow more informed variable rate seeding prescriptions in the future. Dave Bassett, one of the cooperators stated, “We were able to do all our variable-rating with our soybean planter on the fly. We learned we were seeding a little bit higher than we needed to be and that there would be an economic advantage to lowering our seeding rates.” There was no significant yield increase with seeding rates higher than 110,000 seeds per acre. There were five other 2019 studies conducted on field length strips (varying seeding rates from 80,000 to 180,000 seeds per acre) 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 (no final stand counts are available).

With more growers planting soybean early to capture yield benefits, we’ve received questions about the seeding rate needed when soybean is planted early. Planting date (April vs. May) by planting rate (90K, 120K, 150K, 180K seeds per acre) on-farm research studies showed no yield difference from soybean planted in April or May with seeding rates of 120,000-180,000 seeds per acre. In those studies, the seed was always treated with a fungicide and insecticide seed treatment. Bottom line, with 36 studies conducted, 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).

A seeding rate of 120,000 seeds per acre has performed well across counties, farms, and fields in Nebraska.

Recommendations from neighboring states agree with the findings of the Nebraska On-Farm Research Network. 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; yield was maximized with 127,000 plants per acre in low yield environments and around 100,000 plants per acre in medium and high yield environments. Regional research data has concluded that 100,000 plants per acre at harvest is a great target.

Considerations

If you plant between 140,000 and 160,000 seeds per acre, consider dropping your seeding rate to 120,000 seeds per acre and aiming for a final plant stand of 100,000 plants per ac based on our research findings.

  • 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.

If you plant at 180,000 or more seeds per acre, consider dropping your seeding rate to 140,000 seeds per acre as a step-wise increment.

  • 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 purchasing hail insurance too costly of a risk management plan? Afraid of planting 120,000 seeds per acre? Try this… purchase the hail insurance, use fungicide-treated seed, but reduce the seeding rate down to at least 140,000 seeds per acre, which is one unit or bag per acre.

You can also test this for yourself by conducting your own on-farm research study (protocol here). 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.

References

Ciampitti, Ignacio. 2018. Soybean seeding rates and optimum plant populations. Kansas State University Extension.

De Bruin, Jason and Palle Pederson. 2008. Soybean seed yield response to planting date and seeding rate in the upper Midwest. Agronomy Journal. 100:696-673.

Licht, Mark. Soybean Plant Population. Iowa State University Extension.

Rees, Jennifer and Jim Specht. April 10, 2009. Why Soybean Planting Date Does Matter in Nebraska, University of Nebraska Extension CropWatch.

Rees, Jenny, Laura Thompson, Nathan Mueller. April 2018. What On-Farm Research has Taught Us about Soybean Seeding Rates.

Specht, James, Patricio Grassini, Jenny Rees, Nathan Mueller, and Roger Elmore. April 19, 2018. Amplifying Positive Impacts of Early Soybean Planting, University of Nebraska Extension CropWatch.

Stepanovic, Strahinja, Justin Richardson, Jovan Radojicic, Ognien Zivkovic, Milica Bogdanovic. March 30, 2020. Seeding Practices and Nitrogen Management for Western Nebraska Soybean: What Matters and Why. University of Nebraska CropWatch.

Thompson, Laura. February 10, 2020. Four Nebraska Farmers Share what They Learned Conducting Farm Research Last Year. University of Nebraska Extension CropWatch.