As grain farmers make the transition from planting corn to soybeans, a Purdue Extension soybean specialist says they need to keep a few basic principles in mind. Planting conditions and timing, seeding rates and depths, and an awareness of insects play major roles in the crop's yield potential.
"This has been an odd year because some growers were planting soybeans as early as March," reported Shaun Casteel, soybean specialist. "Generally, the optimal planting time would be between the last week of April through the first three weeks of May, depending on location."
Although a cold spell in April and recent rains have delayed field operations a little, Casteel said growers don't need to worry. "There is plenty of time yet to plant soybeans during the optimal window, even with the rain," he said. "The fields will dry out and growers will be back in the fields this week or next."
As farmers head back out to resume planting, Casteel said soybeans should be planted between 1 and 1.5 in. deep, depending on field conditions. If the soil is dry, seeds should be planted closer to the 1.5-inch mark. In wet soils, they should be planted shallower.
The seeding rate, he said, will depend on the type of planting equipment and how well it sets seeds. "Optimum plant population is about 100,000 to 120,000 plants per acre, which means we need to plant about 140,000 to 160,000 seeds (or about 125,000 to 145,000 viable seeds) in most instances," Casteel said. "If the equipment isn't as good, plant more."
He also suggested planting into a clean seedbed. While most growers completed burndown in a timely fashion, some fields might be in need of the postemergence application earlier than normal. Growers who opted for a residual burndown treatment, however, will have a longer window before the first postemergence application.
In addition to weed control, Casteel said soybean growers need to keep a close eye on bean leaf beetle. At this point in the growing season, early-emerged soybean plants are most at risk. "If you do find bean leaf beetle, keep the tolerance thresholds in mind," he said. "Use an insecticide application if leaf defoliation is greater than 40%."