Soybean Yield Response to Seeding Rate in Eastern Canada

• In 2023, soybean growers in eastern Ontario experienced a severe outbreak of white mold disease in soybeans.
• This outbreak generated interest among growers in population management as a tool to reduce white mold disease pressure.
• An experiment was conducted in 2024 to evaluate the effect of seeding rate on soybean yield in Eastern Canada.

• Locations: 19 co-operators sites in Central/Eastern Ontario, Quebec, and New Brunswick (Figure 1)
• Plot Layout: Field-length strips
• Replicates: 1-2 per locations
• Pioneer^® brand soybeans¹: P05Z60E™, P06A38E™, P07T59E™, and P17A87E™
• Experimental Factor
  • Seeding Rates: 80,000, 120,000, and 160,000 seeds/acre

¹All Pioneer products denoted with ™ are brand names.

Growing Season Conditions and Stand Establishment

• The 2024 growing season was above average for soybean yield in Eastern Canada. In local variety plots in the area, yields were generally around 5 bu/acre greater than normal.
• Adequate rainfall through the growing period, especially in August, aided in producing higher yields.
• White mold, the number one soybean disease in the study area, generally remained at low pressure levels.
• Adequate moisture during and immediately after planting allowed for excellent stand establishment, averaging 90% of seeding rate (Figure 2).
• In dry or tougher conditions, lower stand counts versus what was planted would be expected. Growers need to adjust seeding rates based on yield environment, crop rotation type, residue cover, tillage practices, and planting date.

  

  Figure 2. Soybean stand establishment (actual and percentage) by seeding rate.

Soybean Yield

• Seeding rate did not have a large impact on final yield.
• Yield at the 80,000 seeds/acre rate was significantly lower than yield at the 160,000 seeds/acre rate, but neither significantly differed from the 120,000 seeds/acre rate (Figure 3).
• With so little yield difference between the lowest and highest seeding rate, further sampling was done to investigate how other yield components were compensating for the lower number of plants per acre.

  

  Figure 3. Soybean yield by seeding rate. Bars without the same letter are significantly different at α=0.05.

Soybean Yield Components and Characteristics

• Seed samples were collected at 14 of the study locations to measure seed weight across the different seeding rates.
• Results showed that seed weight did not differ among seeding rates (Figure 4).

  

  Figure 4. Soybean seed weight in seeds/lb by seeding rate. (No significant differences at α=0.05).

• Plant samples were collected from each seeding rate treatment at one location to quantify seeding rate effects on the number of pods, nodes, and trifoliates per plant and seeds per pod.
• Plant samples were comprised of 10 plants selected at random from each seeding rate treatment.
• There were not large differences among seeding rates in seeds per pod, but there were in pods per plant (Table 1).

  Table 1. Soybean yield components and plant characteristics sampled at one study location.

  Seeding Rate	Pods	Nodes	Seeds per Pod	Trifoliates
  80	63.6	26	3.04	25.0
  120	39.2	16.2	2.94	14.0
  160	29.2	12.4	2.82	14.3

• The average number of pods per plant at the lowest seeding rate was more than double that at the highest seeding rate, making it clear that pod number was the yield component playing the greatest role in compensating for the lower number of plants per acre (Figure 5).

  

  

  Figure 5. Soybean plants sampled from the 80,000, 120,000, and 160,000 seeds/acre seeding rate treatments (top) and the same plants with the leaves and pods removed (above).

• Nodes and trifoliates per plant both differed substantially between the lowest and middle seeding rate, but to a much lesser degree between the middle and highest seeding rate.
• Stem diameter measurements taken at two locations showed a similar pattern, with a larger difference between the lowest and middle seeding rate and and smaller difference between the middle and highest seeding rate (Figure 6).

  

  Figure 6. Soybean stem diameter by seeding rate.

  

  Figure 7. Soybean stem diameter measurements on plants taken from the 80,000 seeds/acre seeding rate treatment (left) and the 160,000 seeds/acre treatment (right).

• Growers need to look at all aspects of stand establishment when considering a soybean seeding rate. There is no one “catch-all” population recommendation. Yield goals, disease management strategies and planting conditions all play a role.
• Yield environment is the most critical factor in setting soybean populations. As yield potential increases, soybean populations can be reduced due to larger plants and more nodes per plant which leads to more pods per acre.
• Variable rate seeding is an efficient way to manage soybean population across different yield and moisture holding environments within a field.
• Population is one factor to consider when trying to maximize soybean yield in a white mold disease environment. More research is needed to better refine soybean population recommendations for the future.

  

  

  Figure 8. Leaf senescence began later in the 80,000 seeds/acre seeding rate treatment (left) compared to the 160,000 seeds/acre treatment (right).