Corn Count

Purdue Study Pinpoints Optimal Corn Plant Population

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Do you know how many plants are surviving from your seeding rate? A 95% stand count is achievable, Purdue University researchers say. (DTN photo by Bryce Anderson)

ROCKVILLE, Md. (DTN) -- The corn plant is slowly shedding its reputation as the high-maintenance diva of the crop world.

"Breeders have done one thing primarily -- increase the stress tolerance in hybrids today," explained Purdue University corn agronomist Bob Nielsen. Along with his colleagues, Nielsen recently crunched the numbers on 81 field trials in Indiana since 2008 and re-affirmed the corn plant's growing tolerance to a wide variation in planting populations.

"The result is if we want to keep increasing seeding rates, we can do so with minimal risk of losing yield, but on the flip side, we can also lower rates without as big a yield decrease as we used to get," he said.

The researchers determined that, under normal growing conditions in Indiana, the optimal agronomic plant population was around 31,600 plants per acre. Under stressful conditions -- such as drought or flooding -- the optimum plant population dropped to around 21,000 plants per acre.

However, Indiana farmers can safely go lower than that without losing much yield, Nielsen noted. The economic optimum planting populations is almost always "several thousand lower" than the agronomic optimum, he said.

"These hybrids are so tolerant of population that when you get near optimum plant population, the yield response flattens out and almost goes to zero," he explained. "You just cannot afford to put on more seed when in essence you're getting nothing in return."

All the Purdue field trials were planted with 30-inch row spacing, and plant populations ranged from 25,000 to 42,000 plants per acre.

The Purdue researchers calculated optimum seeding rates with the assumption that 95% of the stand would survive, Nielsen explained. So to target 31,600 plants per acre at harvest, a grower would plant around 33,250 seeds per acre (Divide the desired plant population by 0.95).

If growers are getting thinner stands than 95%, they will need to add more seed or, better yet, work on improving that final stand count, Nielsen said.

"We're encouraging growers to track final plant population themselves" in every field each year, he said.

He recommends waiting until V6 to estimate a final stand, which can be done by counting plants in 50- or 100-foot intervals.

Growers also need to verify that their planter is accurately dropping the population they've selected, Nielsen said. "I'm not sure people regularly double check their monitor is accurate, to make sure that if it says they're dropping 33,000 seeds per acre, that is indeed what they're planting."

In 27 of their 81 field trials, the Purdue researchers planted pairs of hybrids from eight seed companies categorized as more or less responsive to plant populations.

They found no consistent differences in how these hybrids responded to plant population, Nielsen said.

"What that tells us is these ratings are not black and white and are easily influenced by growing conditions," he said.

In eight of the field trials, the researchers also tested the farmers' normal nitrogen rate against a bulked-up rate 50 to 75 pounds above it, to see whether higher nitrogen rates influenced a field's yield response to plant population.

"What we found was -- within the range of populations we considered (25,000 to 42,000) -- as long as you are already using what we believe to be optimum nitrogen rate, simply adding more nitrogen does not improve any yield response to population," Nielsen said.

To see the researchers' summary of their field trials, visit this Purdue webpage:…

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Emily Unglesbee