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Corn+Soybean Digest

Plant Population PAYBACK

With seed corn costs escalating, particularly among transgenic hybrids, farmers may be tempted to scale back on plant populations a bit to save costs. However, that would be a big mistake for most farmers, warn a pair of university agronomists.

“Even with yields as low as 100 bu./acre, you can pay up to $130/bag of seed and still have a slight return from a higher plant population (30,000 vs. 28,000 plants/acre) selling grain at $2/bu.,” says Dale Hicks, University of Minnesota Extension agronomist. “For yields at 120 bu./acre and higher, you can achieve a positive return from higher plant populations with seed costs as high as $150/bag.”

In Minnesota, research shows corn populations should be between 29,000-31,000 plants/acre at harvest to produce the maximum grain yield.

“To achieve this final stand, I suggest increasing kernel drop by 15% when planting corn prior to May 1 for a drop of about 34,000 to 35,000 kernels/acre,” says Hicks. “After May 1, a 10% increase is sufficient for a drop between 32,000 and 34,000 kernels/acre.”

Increasing kernel drop by about 5% when planting early is typically good insurance, adds Hicks. The reason is soil temperatures are much lower in Minnesota when planting in April than in May. Thus, there is greater risk that some kernels may fail to successfully germinate, emerge and produce the desired stand to maximize grain yield.

Bob Nielsen, Purdue University Extension agronomist, agrees that boosting plant populations when planting early can sometimes be beneficial. However, using a starter fertilizer may be even more important than boosting plant populations, he says.

“If from experience, early planting reduces stand establishment, you might want to bump plant population by 5% or so, particularly if you're planting aggressively early,” he says. “When planting aggressively early, however, start with exceptional seedling-vigor hybrids, plant high-quality seed and use a starter fertilizer of no less than 20 lbs./acre.”

Using a starter fertilizer when planting early in Minnesota is also a good practice, says Hicks. “Especially with cold soils and early planting dates, starter fertilizer provides a nice yield response,” he says. “It also provides much greater stand uniformity.”

Final plant stands throughout Indiana should be about the same as in Minnesota, although the recommended seeding rate may be a little lower, says Nielsen. “For the majority of our soils, and those in adjacent states, the final plant population should be close to 30,000 plants/acre,” he says. “Seeding rates should be between 32,000-33,000 plants/acre.”

However, on poor soils that yield consistently below 120-125 bu./acre, Nielsen advises reducing seeding rates to achieve harvest stands between 24,000-25,000 plants/acre. Minnesota's Hicks gives similar advice.

“The main exception to our state's recommended plant population rates would be on non-irrigated, sandy soils,” he says. “In those fields, we recommend a harvest plant population between 22,000-24,000 plants/acre.”

In comparison, the optimum harvest population on most irrigated fields in Minnesota is between 34,000-35,000 plants/acre, says Hicks. He adds that university recommendations for corn plant populations are continually being revised for both irrigated and non-irrigated fields as newer hybrids are developed to yield better under stress. As a result, he advises farmers to consult with their seed dealers to find out whether some hybrids might yield better than others at higher plant populations than normally recommended.

While cost will always be a factor when considering seed, many other factors are typically more important, emphasizes Hicks.

“Seed cost should be the last consideration after hybrids are chosen,” he says. “The key characteristics to examine include yield potential, maturity, moisture at harvest, resistance to diseases, insects, herbicides and stalk quality.”

This year, fertilizer costs will likely be more expensive than normal. However, even if fertilizer costs were low, overall nitrogen (N) rates don't need to change if boosting plant populations for early planting, says Nielsen.

“If by virtue of increasing the seeding rate, you consistently obtain higher yields, then it makes sense to increase fertility,” he says. “However, most people are over-fertilizing anyway. Especially with today's N prices, if you're upping plant populations by only 4,000-5,000 plants/acre, that won't change N requirements much.”

Costs for equipment would likely be prohibitive for most farmers considering an investment in variable-rate planting technology that would allow them to vary plant populations on the go. “The bottom line with variable-rate planting is that it's just a seed-saving mechanism,” says Hicks. “Typically, the potential savings in seed cost alone would nowhere near justify the cost of the technology.”

Nielsen agrees. “Variable-rate seeding would only make sense for the farmer whose range in yield levels within fields vary to the extreme,” he says. “Then the only merit is in reducing the plant population for low-yielding areas.”

Farmers who are concerned about proper plant population should carefully examine hybrids and fields at harvest.

“If you consistently see multiple ears on stalks or ear sizes that are unusually large, that is an indicator that plant populations might be too low,” says Nielsen. “If plant populations are too high, problems with barrenness can result. However, a much more common indicator that plant populations are too high is to have perennial problems with stalk quality and standability.”

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