For many farmers, the answer to the question of when to start planting soybeans usually has been “when I’m finished planting corn.”

That attitude, however, is starting to shift as farmers begin managing soybeans more intensively in pursuit of higher yields.

In research trials covering 130 locations in 18 states last year, planting date proved to be a key factor for higher soybean yields, according to DuPont Pioneer field agronomist Brian Bush.

The ideal planting date for soybeans in the Upper Midwest was between May 5-8, he said. After mid-May, soybean yield potential started to decrease.

“Fertility is critical for...