What should your soybean seeding rate be?

“I love getting this question from growers - What should my seeding rate be?” says Marijke Vanderlaan, Agronomic Service Representative with Syngenta. “Ultimately it depends on three points: your soil type, the variety you are growing and the yield environment you are in. Then, fine tune your rate based on your equipment and history of disease”.

Syngenta has developed a population matrix that can be found here to provide growers with a tool to help make your seeding rate decision. The matrix provides a final stand count based on your soil type and yield environment, and the type of soybean you are growing eg. thin vs bushy in stature.  

Syngenta soybean seed population matrix, 2021 NK® Seed Guide

Understand your farm first

Before you can use the population matrix, you first need to understand what the difference is on your farm between your seeding rate and your typical final stand. “Often this difference or ‘gap’ is a lot higher than you think”, says Vanderlaan. She adds “It’s not uncommon to see a 10-30% difference depending on whether you use a planter vs drill, conventional till vs no-till, sand vs clay”.   

After you have chosen varieties based on suitability to your management practices, soil type or field history, it’s important to review your seed guide and understand the ability for that variety to branch.  

Studying soybean population dynamics

Over the last four years, Vanderlaan has conducted soybean population trials with various growers to better understand soybean population dynamics and the how the ability of a soybean variety to branch is connected to seeding rate. This question becomes even more important if a grower is on 30” rows. In this case, Vanderlaan recommends choosing a variety that is well suited to 30” rows, meaning it has the ability to branch in response to its environment.

In 2017, Vanderlaan conducted a trial with a grower near Lowbanks, ON who was growing soybeans in 30” rows in a high yielding environment (approximately 60+ bu/ac) to dig deeper into these questions. The grower chose a variety with a branching architecture and planted a replicated strip trial with the following populations: 80,000, 120,000, 160,000 s/acre. 

In the trial results, the grower saw very little difference in yield, but did see improvements in standability at lower seeding rates. At the highest seeding rate, the canopy closed about week sooner than the lowest seeding rate. It was concluded in this environment, with a very low “GAP” between seeding and final stand, the optimal seeding rate was 120,000 s/acre.

Digging deeper into branching characteristics

Over 2018-2019, Vanderlaan wanted to better understand soybean branching characteristics. She worked with a grower near Ayr, ON to assess the branching capability of one of NK’s most popular traited varieties, S20-L8X. They looked at various seeding rates from 100,000 to 160,000 s/acre in 30” rows planted into long-term no-till conditions. Here they saw a difference of 15-25% loss from planting to final stand. An interesting discovery found in these trials was that for every 20,000 to 25,000 plants/ac less, the variety would grow an additional branch. However, there was very little difference in yield between the seeding rates.

In 2020, Vanderlaan worked with another grower near Drumbo, ON to look at the branching capability of a new variety in the NK® soybean portfolio, S20-E3. It was planted into 30” rows of a no-till environment to see if it would respond similarly to NK® variety S20-L8X. Findings were in fact similar, and very good branching characteristics were observed.

See chart and images for reference:

Final Stand Count (Plants/acre)	Branches per plant
64,500	4.3
91,000	3.6
121,000	3.1
222,500	0.9

Photo taken in Drumbo, ON by Marijke Vanderlaan. 

Summary

Over the last few years through many trials conducted with growers in Ontario, Vanderlaan has observed that Syngenta’s population matrix is an effective tool to help growers dial into the right population for their farm. For more information on using the population matrix and to determine which variety is right for you, please speak to your Syngenta representative. If you’re unsure of who to contact, this handy Find My Rep tool will help you out.