The Soybean Watch ’21 field was no-tilled into cornstalks on May 15. More than an inch of rain followed within a couple of days. That caused some crusting in soils with relatively lower organic matter, even in no-till. Plus, coming out of a very cool period meant soil temperatures weren’t as warm as usual in mid-May.
As a result, when the grower checked the field seven days after planting, he had reservations about whether enough beans would emerge to keep the stand. Yet 10 days after planting, more soybeans were emerging. It wasn’t yet the stand he was accustomed to seeing, but he left the field believing the stand would likely be good enough to keep.
He used a 30-inch hula hoop and threw it at random, and then counted plants inside the hoop. Using the Purdue University Corn & Soybean Field Guide, he determined approximate stands. The guide contains a chart that allows you to convert from number of plants found within the hoop to total plant population per acre without doing the math. Most counts inside the 30-inch hoop were within the 9 to 11 range, which represents 80,000 to 98,000 plants per acre. Outliers were as low as 62,300 and as high as 142,000. Seeding rate was around 145,000 seeds per acre.
“I advise growers they should be OK with 80,000 plants per acre if there aren’t huge gaps and they can control weeds,” says Steve Gauck, a regional agronomy manager for Beck’s, based near Greensburg, Ind. Beck’s sponsors Crop Watch ’21.
In fact, there is some evidence based on Beck’s Practical Farm Research studies at multiple locations that stands as low as 70,000 still may reach maximum yield potential. Beck’s will continue looking at lower populations to see if it can duplicate those results.
Gauck had not yet seen the Soybean Watch ’21 field at press time. However, based on information from the grower, the stands sounded acceptable in general, and too strong to worry about replanting or adding in more seed.
“When you get to late May or early June, calendar date becomes a factor even if it was a close call on keeping a stand,” Gauck notes. “Beck’s data and university data both show that as you move into late May or early June, odds for reaching full yield potential diminish. Late-planted beans will yield better in some years than others, and you don’t know which year is which when you plant, but there is clear evidence that on average, yields tend to decrease, especially for June-planted soybeans.”
There are three varieties from two different companies planted in the Soybean Watch ’21 field. All three are in the mid-Group 3 maturity range. Based on his observations at 10 days after planting, the grower could not determine a clear difference in total plant emergence between the varieties.
Both corn and soybeans tend to emerge over a longer period if soils crust or if temperatures are cooler. Uniformity of corn emergence is discussed more than in soybeans.
“We would like to see soybeans emerge uniformly, but since populations are much higher, it’s tougher to monitor day by day,” Gauck says. “We also don’t have good data on how much, if at all, uneven emergence affects soybeans.”