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Plant more corn per acre

Agriculture.com Staff 07/06/2010 @ 4:28pm

Just as the commodity markets are telling you to plant more acres of corn, research and economics are telling you to plant more corn per acre. That's partly because seeding rates have been lagging the past few years and partly because those extra bushels you can raise by planting more seed promise to be worth significantly more in the near future than they have been in the recent past.

Obviously, with higher corn prices you can afford to buy a little more seed if you can boost yields.

As a general rule, agronomists throughout the Corn Belt recommend a final stand of 28,000 to 32,000 plants per acre in average- to high-yielding environments.

The National Agricultural Statistics Service conducted yield surveys in 10 corn-producing states in 2006. They visited randomly selected plots monthly from August through harvest and conducted stand counts, among other things.

Most of the fields they surveyed were at the bottom of the optimum population range or below it. (Granted, some of the fields might have been in lower-yielding environments.)

The November stand counts for Illinois showed 28,000 plants per acre, up from 26,350 in 2002.

"Most producers should be aiming to establish 28,000 to 32,000 plants per acre on average to above-average fields," says University of Illinois agronomist Emerson Nafziger.

In Indiana, the November population count was 26,350 plants per acre, up from 25,300 in 2002. Purdue University agronomist Bob Nielsen has conducted several population studies in recent years. "Most of those trials support our current recommendation to target final stands from 28,000 to 32,000," he says.

In Iowa, the November number was 28,600, up from 26,700 in 2002.Roger Elmore, Iowa State University Extension corn specialist, says, "We think people should target 32,000 plants per acre and do what it takes to get that. I tell people if their planting rates are the same as they were five years ago, it is time to change!"

In Ohio, the stand count in November was 26,200, up from 24,400 in 2002. Ohio State University agronomist Peter Thomison says, "On productive soils, with average yields of 160 bushels per acre or more, final stands of 30,000 or more may be required to maximize yields. Planting rate or population can be cut to lower seed costs, but this approach typically costs more than it saves."

If the seed-to-corn price ratio is .5 (see example in Table 1 and the line left with the blue box), the optimum harvest population is 36,000 plants per acre. The yellow error bars represent the range of populations that will return within $1 per acre of optimum. The dollar values on the vertical axis indicate the return to seed cost for each dollar per bushel of selling price. For a seed-to-corn price ratio of .5, return is at a maximum of $180.

To determine the price ratio to use in Graph 1 (above), divide the cost of 1,000 seeds by the selling price of a bushel of corn. For example, if 1,000 seeds cost $1.50 ($120 per bag) and corn is selling for $3.00 per bushel, the ratio is 0.50.

There were similar patterns in the other six states. Minnesota had the highest November population at 28,900, only 1,100 below the 30,000 that University of Minnesota agronomist Dale Hicks says is optimum.

To get a final stand of 28,000 to 32,000, you would typically need to drop 5% to 10% more seed in good conditions and even more under stressful conditions. Another 10% would boost the planting rate range from just under 31,000 kernels per acre to just over 35,000 kernels per acre.

Top yields, and quite often top economic yields, come at the upper reaches of those planting and final stand ranges.

Elmore says yield increases for the past 50 or 60 years have come from more plants per acre rather than from more grain per plant. "Increasing seeding rates has been paramount to increasing yields."

Thirty or 40 years ago, planting even a little bit above the optimum population often led to barren stalks and sometimes lodging.

Constantly better genetics have removed most of that risk.

"Yields tend to level off as population increases, but yields don't really decrease until the population is exorbitantly high," explains Kurt Thelen, Michigan State University Extension specialist. "This means the only punishment for planting at a population that is a bit too high is the increase in seed cost."

Just as the commodity markets are telling you to plant more acres of corn, research and economics are telling you to plant more corn per acre. That's partly because seeding rates have been lagging the past few years and partly because those extra bushels you can raise by planting more seed promise to be worth significantly more in the near future than they have been in the recent past.

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