Nearly 10 years ago, an agronomist predicted that someday farmers would plant corn and soybeans at the same population. He suggested it would be around 50,000 plants per acre. His future isn’t here yet, but the trends are headed in that direction.
Steve Gauck’s cutoff today, when assessing whether a thin soybean stand needs to be replanted, is around 80,000 plants per acre. If weeds are controlled and there isn’t an abundance of large gaps in rows, he’s confident in leaving the stand instead of replanting. Gauck is a sales agronomist for Beck’s, based near Greensburg, Ind. Beck’s sponsors Soybean Watch ’17. Gauck periodically visits a soybean field in central Indiana and reports what he finds.
This year’s soybeans were no-tilled into cornstalks on June 6. On an early visit in late June, Gauck found slugs had thinned the stand. In fact, slugs were still present, and they remained in the field until the last week of July. But by that point, they were no longer a threat to the plants.
“We did stand counts and found that in some of the hardest-hit spots, the population was thinned to about 80,000 plants per acre,” Gauck says. “Plants were healthy with good nodulation, and there weren’t large gaps in most places. It would have been really late to replant at that point. However, I would have left the stand anyway — 80,000 plants are enough to get the job done.”
Why 80,000 works
Later in the season, Gauck returned to the same spot where he had counted 80,000 plants per acre. He pulled a plant from an area that was somewhat thicker and a plant from an area that was thinner. Then he compared the two plants to explain how soybeans can compensate and make up for missing neighbors.
“The plant from the area with more plants was slightly taller, but it had only one branch with pods on it,” he notes. “Many times when soybeans are planted relatively thick, you don’t get plants with many branches that actually produce pods. If branches don’t produce pods and soybeans, they simply waste energy which could have been better used forming pods and beans.”
Gauck looked carefully at the plant pulled from the area where soybeans weren’t quite as thick. Overall plant height was shorter. It had three branches, and all three branches contained pods.
“There was something else going on there,” Gauck adds. “I measured the difference between nodes on the main stem of each plant. The distance was shorter for the plant with more room, meaning nodes were closer together. Nodes are where pods form.”
Overall, there were more pods on the somewhat shorter plant pulled from the area with more elbow room, Gauck reports. In fact, a quick count revealed there were about 50% more pods on that plant compared to the one pulled from an area where plants were closer together.
“Don’t write off soybeans just because you didn’t get the perfect stand you wanted,” Gauck emphasizes. “Late-season weather through September is important, but thinner stands could still produce good yields.”