It is a proven fact that thin soybean stands tend to recover better and yield a higher percentage in relation to original potential yield than corn stands that are thin. But it's also a fact that there are times when soybean stands, whether thinned by seed germination problems, hail or whatever else, can be so thin that replanting might be a better option. How uniform the stand is and whether you can control the weeds, which is usually less of an issue with Roundup Ready soybeans today, can come into play.
Turn to the Purdue University Corn & Soybean Field Guide for help in deciphering whether the counts in your field justify replanting or leaving the original stand. It's published annually by the Purdue Crop Diagnostic Training Center, headed by Corey Gerber. If you don't have a copy, contact your local Extension office, or 1-888-EXT-INFO.
Much of the original work proving how well soybeans could compensate for thin stands was done by Marv Swearingin, a Purdue agronomist, in the '80s. In 30-inch rows, 80,000 plants per acre, if spread fairly uniformly through the rows, can still achieve 100% of the yield potential if planted at full rate with good emergence. In solid-seeded rows, which are more prevalent today, expect about 96% yield at 80,000 plants per acre. What's striking is that at 60,000 plants per acre, you can expect 94% in 30 –inch rows and 92% of original yield potential for a full stand in solid-seeded rows.
If you see 60,000 plants per acre, your first instinct will be to tear up; the stand. Even companies such as Beck's Hybrids, Atlanta, pushing lower seeding rates, still suggest around 130,000 or slightly more seeds per acre. Yet what the data shows is that achieving just 60,000 plants per acre can produce 92% of yield. If your goal was 60 bushels per acre in solid-seeded soybeans, that means you could still achieve about 55 bushels per acre.
Replanting is not free, depending partly upon what type of replant policy your company offers on seed if you need to replant. There are also fuel and equipment costs to consider. Most trials and farmer experiences report that spotting in along existing rows might seem like a viable compromise, it seldom benefits yield vs. just leaving the original stand.
The problem is that while some contend soybeans aren't affected as much by planting date delays as corn, data indicates yields do begin to drop off as you push late May and into early June. You can likely point to years that were exceptions and where soybeans yield very well planted late. The unanswerable question in those cases is what yields would have been if the soybeans had been planted earlier.
According to Purdue data published in the guide, planting May 30 gives you the chance for 96% of full potential with a mid-season variety and 94% with a full-season variety. By June 10, it's 92% and 90%, respectively.
The catch, however, is that assumes a good stand the second time around. With summer thunderstorms that can produce beating rains, there is no guarantee of a good stand, or even a better stand, if you replant. Remember, farming doesn't come with guarantees.