What are you paying for a unit of seed corn? Now that you have that number in mind, let me ask you would rather plant 28,000 population and get a 220 bushel yield, or 40,000 population and get a 225 bushel yield?

Which planting rate gives you the best return? That is a question you have probably never addressed before, so if you are on a rip and tear this year to reduce production cost, let’s explore a new concept.

Grandpa planted checked corn at 12,000 plants per acre. You probably doubled that population in the 1980’s. But as trendline yields have increased, has the yield response been from higher population or from better performance by the corn plant? Iowa State researchers report that your planting population has done more to increase your yield than the corn has contributed.

Now before we get a bushel of complaints from the talented corn breeders around the Midwest, let’s make sure where their efforts have been focused. Iowa State’s Don Duvick and his former colleague Dale Farnham report that trendline yield has not been a function so much of bigger ears of corn, but of the ability of the corn plant itself to perform in a more dense population. In a recent Integrated Crop Management newsletter, Duvick’s research shows “that approximately half of the annual yield increase is due to plant breeding efforts and the other half is due to improved crop management practices.” So pat yourself on the back for getting that bag of seed corn to bolster your income.

The jury is still out on the question of whether corn breeders are responding to the demands of your populations, or whether today’s corn is able to withstand higher populations and you are just forcing the issue a bit. Regardless, the fact is that planting populations are climbing along with trendline yields. But as the price of seed corn increases, planting more seed will reach a level of wasting money, just like dumping on nitrogen without a yield response that returns money to your pocket.

This may be a new concept, a concept of a “maximum return to seed” just like a “maximum return to nitrogen” or a return to any other resource you contribute to the crop, even a return to labor and management. The Iowa State research on a maximum return to seed (MRTS) has two findings: “First, as seed price increases, MRTS decreases. Second, the decrease in MRTS is more evident at the 180 bushel yield level than with the 220 bushel yield level. With the lowest seed price, a seeding rate of 33,000 resulted in the highest MRTS for both yield levels. Yet, as seed price increases, seeding 3 to 6 percent fewer seed (1,000 to 2,000 fewer seeds per acre) results in the highest MRTS.” Think about a curve on a graph that peaks at a certain point then begins to turn downward. Your population target should be the peak of the curve, not after it turns downward, which is where you are wasting money by putting more seed in the ground and not getting the per acre yield response you expect.

Summary:
Because of high nitrogen prices this year, the efficient producer will be applying a rate of N that gives him a maximum return, which reconciles the price of the N and the market price of corn. This is the same concept for determining a population rate, which gives the maximum rate of financial return, defined as a “maximum return to seed.” Every resource used on your farm should be adjusted to its maximum rate of return. Planting population is no different than machinery, labor, or nitrogen, since the cost of the seed can be balanced against the revenue from the expected yield.

Stu Ellis

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