Armstrong Research and Demonstration Farm
Modern, elite soybean varieties respond well to early planting. Multiyear results from ISU research farms suggest that mid-April to early May planting dates most often produce top yields. Research farm and on-farm strip trials also suggest that elite varieties yield similarly over a wide range of seeding rates and resulting harvest populations. Based on these results, producers are advised to plant soybeans as soon as spring field conditions allow, with a seeding rate of 150,000–175,000 seeds/acre.
Iowa State University
Lundvall, John; Westgate, Mark E.; Whigham, Keith; and Farnham, Dale E., "Soybean Response to Early Planting and Seed-applied Fungicide" (2002). Iowa State Research Farm Progress Reports. 1574.