Investigating the effects of seed treatments on the economically optimal seeding rate of conventional soybean in Atlantic Canada

Soybean seeding rates in the cool growing environment of Atlantic Canada are much higher than other regions impacting economic return. Recent studies across North America have suggested that soybean seeding rates can be lowered to maximize profitability. Seed treatments have been shown to improve abiotic stress tolerance and may be another mechanism to reduce seeding rates. Therefore, the objectives of the present study were to (i) determine the economically optimal seeding rate (EOSR) for conventional soybean in Atlantic Canada and (ii) determine if fungicide seed treatments can reduce this rate. Field studies were conducted in 2020 and 2021 to evaluate the effects of four seeding rates and four fungicide seed treatments on soybean stand establishment, growth, resource use efficiency, yield, and profitability. Price received had a dramatic effect on producer return and the EOSR which ranged from 243,000 seeds ha-1 under a low price received scenario ($0.45 kg-1) up to 613,000 seeds ha-1 under a high price received scenario ($0.82 kg-1). In contrast, seed and pesticide costs had a minimal impact on expected returns. Soybean resource use efficiency was not impacted by seeding rate or by seed treatments. Further seed treatments did not impact soybean stand establishment or profitability. Soybean yield increased with seeding rate and plateaued at a seeding rate of 741,000 seeds ha-1 whereas individual plant yield dramatically declined as seeding rate increased. Results of this study suggest that soybean producers in Atlantic Canada should base their seeding rates on contracted or expected price received to maximize profitability.