Impact of Planting Date and Seed Treatment on Soybean Yield

Today’s high-yielding soybean varieties respond favorably to early planting. Multi-year results from statewide university research farms suggest that mid-April to early May planting dates produce top yields in most comparisons. 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 to 175,000 seeds per acre. The yield response of modern varieties to early planting raises questions about expanding the soybean planting season (very early planting of some soybean acres in late March or early April) when weather conditions allow. In 2000 a soybean “planting date x seed treatment” study was initiated to evaluate yield response of two adapted, high-yield varieties to very early planting. Research objectives are to determine whether planting soybeans earlier than corn could be a viable management option for Iowa producers, and if fungicide seed treatments are needed to make this practice profitable. Establishment of similar studies at four other university research farms statewide afforded yield response comparisons of adapted varieties from five unique soil associations and environments. Soils at the Armstrong Research Farm are typical of the Marshall-Exira soil association