Soybean stands can suffer from a wide variety of problems that will reduce population. Hail, diseases, insects, cold soil temperatures at planting, compaction, and planter failures can all affect the stand individually and in combination.
Stand reductions almost never occur evenly across the field. Here are some basic steps to help evaluate soybean stands and decide if re-planting is necessary.
Take 10 stand counts in the area with the worst damage and 10 counts in the part of the field that was not affected or affected just slightly. At each point, measure off 10 feet of row and count the number of live, viable plants. Then calculate the average of your 10 points and compare them to the table below to see how many plants per acre you have remaining.
A stand of 100,000 evenly distributed plants generally gives you optimum yield. As the growing season progresses, however, it is much more difficult to establish a good stand. A stand of 75,000 on May 15 is inadequate, but you might be better off leaving a stand of 75,000 plants if it is July 1.
Planting soybeans on or before June 1 averages 95% of expected yield. In a five-year Latham Seeds’ study, there was no significant yield difference in soybeans planted before May 15. Planting dates included late April, early May and mid-May. We did not see yields drop to 85% or lower until after June 15.
Our results are similar to studies done by university researchers. If you farm below the line from Watertown, SD through the Twin Cities and over toward Green Bay, Wisc., I recommend staying with soybeans in your normal maturity until mid-June. After June 15, consider the precipitation expected in late June and early July because the biggest threat to establishing a late soybean crop is lack of rainfall. If you are north of that line, you may need to switch to an earlier variety a week or so sooner.
