Research Highlights

Research Highlights
Managing Seed Investments Through Seeding Rate Adjustments

By Barb Baylor Anderson

Soybean seeding rates have been declining during the last 20 years. That’s because farmers have moved away from planting with drills and moved back into rows, seed treatments and herbicide-resistant seed are increasingly in use, and better handling has improved seed quality.

The concern is that the decline in seeding rates comes with production risk. Research funded by the Wisconsin Soybean Marketing Board involving input from 12 states and Ontario sought to quantify the risk associated with changes in seeding rate and plant density across a range of environments and productivity levels in North America and the impact on soybean yields.

“With rapid adoption of geo-spatial tools like yield maps and variable rate seeding during the last decade, our findings will help farmers agronomically and economically better manage their annual seed investment by adjusting seeding rates based upon productivity of the environment and its underlying environmental factors,” says Shawn Conley, University of Wisconsin soybean specialist and principal investigator of the checkoff-funded research.

Conley says previous studies determined that 100,000 plants per acre at harvest are required to maximize yield while others found 75,000 seeds per acre maximize profit. Additional research has suggested plant stands as high as 243,000 plants per acre are needed in drought-prone environments while economically optimal seeding rates can be as high as 130,000 seeds per acre.

“There are a wide range of agronomically and economically optimal seeding rates and plant stands driven by variation in seed costs, grain prices, seed treatment use and, most importantly, the productivity of the environment,” says Conley. “This work suggests there is opportunity for farmers, based upon the environment’s productivity, to maximize yield by adjusting seeding rates at the between- and within-field level, particularly in more northern environments.”

Conley says more than 200 field studies were conducted, grouping fields in similar environment clusters and low, medium or high yield levels. Trials confirmed variable rate seeding technology may help farmers better manage soybean seed investments by increasing seeding rates in environments of lower productivity and decreasing rates where there is higher productivity.

“Agronomically optimal seeding rates (AOSR) should be targeted within each environment,” advises Conley. “From a risk perspective, seeding rates increasingly below AOSR increase potential yield loss. Seeding rates above AOSR provide a slight risk reduction with a negligible potential yield increase but raise seed cost. Particularly in the north, the increase in seeding rate to reach AOSR within lower productivity environments should be relatively greater than the decrease in seeding rate to reach AOSR within higher productivity environments.”

More specifics can be garnered from reviewing study results at

“Ultimately, specific seeding rates for varying levels of productivity across an individual field or between fields will still need to be based on local recommendations for issues like weed control, white mold, iron deficiency, risk tolerance and seed costs,” says Conley. “Regardless of seeding rate implemented, farmers should establish an optimal stand at planting and maintain it until harvest to maximize yield, specifically within low and moderate yield levels.”