If you planted soybeans when it was a bit sticky, or if you got plastered by hard rains, and very few came up, then it's a no-brainer – you will need to replant. However, if you have a stand that's just not what you want, then you ought to think about replanting more carefully. That's the conclusion of Purdue University agronomists and ag economists.
Their findings are summarized in a table in the Purdue University Corn & Soybean Field Guide, prepared by the Purdue Diagnostic Training Center. Learn more at: www.agry.purdue.edu/dtc or order the guide directly.
The surprising thing about soybeans, notes Shaun Casteel, Purdue Extension soybean specialist, is their ability to compensate for missing plants. He is doing work that shows around 120,000 plants per acre is enough for top yield. Most people are still planting 150 to 180,000 seeds per acre in narrow or 15-inch rows.
Casteel writes the Soybean Success column for Indiana Prairie Farmer. He has touched on soybean populations in past issues.
Based on landmark work by Marv Swearingin at Purdue in the 1980's and 1990's, it's clear that soybeans can still compensate and produce a good yield at relatively low populations. Ellsworth Christmas later affirmed the work in similar tests at Purdue.
For example, 120,000 plants per acre and 160,000 plants per acre are rated equal on yield potential after years of testing. And 80,000 pants per acre, only half of the intended stand, can still produce 96% of potential yield in narrow rows, and 100% of expected yield for higher plant counts in 30-inch rows.
Most farmers would tear up 80,000 plants per acre in a heartbeat. The real break begins to occur below 60,000 plants per acre. In drilled rows 60,000 plants per acre can still produce 92% of original yield.
What happens in a replant situation is that you're so late in the season, and you have 80,000 soybeans planted three weeks ago. Replanting now doesn't guarantee a perfect stand. Even if you get it, Purdue data says that if you don't replant until May 30, you're already at 94% of original yield potential. So the odds favor leaving the original stand.