The trend over the past several years, when talking about full-season soybeans and seeding rates, has been to trim rates and plant fewer beans per acre. Shaun Casteel, Purdue University Extension soybean specialist, has helped lead the charge, pointing to his own research that indicates it’s possible to obtain full yield potential at lower seeding rates than once thought.
Now Casteel is talking about planting higher seeding rates if you’re still planting soybeans in 2019. What caused the change?
Casteel assures that he hasn’t changed his mind. The difference is that it’s no longer a matter of planting soybeans that will have a full growing season to produce. The historic planting delays of 2019 have flipped the tables. If you still have soybeans to plant, you need to think about planting more soybean seeds per acre than you normally plant, not fewer, he says.
“It’s all about having as many nodes out there in the field as possible once soybeans enter the reproductive stage and begin producing flowers and pods,” Casteel explains. “When you can’t plant until well into June, soybeans have less time in the vegetative stage, and will tend to produce fewer nodes per plant. Nodes are what produce pods and beans, and give us the higher yields we desire. To compensate, we need to add more plants to get more nodes out there working for us.”
Here’s how Casteel suggests adjusting seeding rates if you’re still planting soybeans. If you routinely plant double-crop soybeans after wheat, the strategy will sound similar.
If you typically plant 120,000 to 140,000 seeds per acre in April or early May and 140,000 in late May, you should have increased the rate to about 155,000 if you planted last week, during the first week of June. That’s assuming you’re using a planter in 30-inch or 15-inch rows. If you’re planting with an air seeder or drill, kick the rate up even higher, since depth placement isn’t as precise, Casteel says.
“Our basic recommendation is to increase seeding rate about 10%, which will be roughly 15,000 seeds per acre, for each week that planting is delayed,” he explains.
So, if you’re planting this week, the second week of June, with a planter, he would increase seeding rate to 170,000 seeds per acre. Next week, bump the rate again, to around 185,000 seeds per acre. If you plant during the fourth week of June, go up to 200,000 seeds per acre, Casteel says.
Remember, these are specific recommendations for a specific situation. When the calendar flips to 2020 and a fresh start, with hopefully a normal planting season, his recommendations will revert to their normal numbers.
If you’re doing calculations to decide whether to switch to soybeans from corn, especially in southern Indiana where full-season corn is still an option, remember to account for increased costs for planting soybeans due to increased seeding rates. Some budgets you may have seen comparing planting corn versus soybeans may not have included increased planting costs for soybeans in the comparison.
Depending on soybean seed cost, increasing all the way to 200,000 seeds per acre in the last week of June could add another $30 per acre compared to planting at the normal time, Casteel concludes.