Suppose your soybean stand isn’t up to par. You planted 140,000 seeds per acre, but Mother Nature didn’t cooperate. You roll your hula hoop in five different spots and find an average of 10.1 plants per hoop. Is that adequate?
Obviously, you can’t answer until you convert to plants per acre. Steve Gauck, regional agronomy manager for Beck’s, Greensburg, Ind., carries the Purdue University Corn & Soybean Field Guide in his pocket. He refers to a chart in the guide. Knowing his hula hoop is 30 inches in diameter, he determines the population is just over 89,000 plants per acre.
“Past experience tells me that’s likely enough plants to deliver at or near maximum yield,” Gauck says. “At that point, I would be inclined to leave the stand, especially if it’s June 1. Even if you replanted June 1 and achieved 120,000 plants per acre, the guide indicates you can only expect about 94% of original yield for a full-season variety. If your yield goal was 60, your replant target is 56.4.”
But “What is my stand count?” isn’t the only question you should ask, Gauck says. Beck’s sponsors Soybean Watch ’20.
“The next thing to determine is how many areas in various rows have skips with no plants,” Gauck says. “And, how long are the skips? Soybeans will compensate for missing plants much better than corn. But there’s still a limit to their ability to make up for missing plants.”
Plus, skips mean more open space where the canopy doesn’t close completely, he adds. You waste sunlight and give weeds a competitive edge. Open space means later-germinating weeds such as waterhemp and Palmer amaranth have an extra advantage.
Skips can result from various factors, including poor seed placement, slug feeding, insect damage and soil crusting. So, just how much can skips hurt yield?
Turning to the Purdue guide, Gauck notes that 2-foot skips, if they make up 50% of the row, can reduce yield expectations. Expect 94% of normal yield.
However, if skips are longer, say 3 feet, covering 50% of the row, you may only achieve 87% of original yield. With extreme 4-foot skips, the potential drops to 85%.
Suppose you have 2-foot skips consistently in that field with 89,000 plants in the opening example. You’re still expecting 60 bushels per acre at 89,000, if evenly distributed. With consistent 2-foot skips, you’re looking at 56.4 bushels per acre, the same as replanting June 1 and achieving 120,000 plants without skips.
“There’s no guarantee you’ll get a near-perfect stand by replanting,” Gauck observes. “If slugs caused the problem, we’ve seen them hang around into late June recently, so they could still cause damage. In this scenario, I wouldn’t replant.”
Ratchet up the length of skips. If you’ve got 89,000 plants per acre with 3-foot skips, you’re looking at 87% of 60 bushels per acre, or 52.2 bushels per acre. At $8 per bushel, you could potentially pick up about $32 per acre if you get a good, even stand on replanting.
“Now you’re down to pushing the pencil harder,” Gauck says. “Does your seed supplier provide replant seed? If not, you may spend more on seed than you could make up, not counting other replant costs.”
Leave crop insurance out of this scenario. “At best case, with the seed supplier providing seed, you’re still likely looking at a toss-up call,” Gauck concludes.