Sort Through Mixed Signals on Planting Date

Take other factors into account.

Published on: Feb 2, 2009

The theme of the High Yield Corn Trial in the Corn Illustrated plot at Edinburgh, Ind., in '08 seemed to be that late planting can hurt yields. The top yield reached on any plot was 200 bushels per acre of dry corn. The trial was planted during the last week of May. One year earlier it was planted May 1, the year was much drier, especially during key times, and the top yield was 245 bushels per acre. The fields were irrigated in both years.

Dave Nanda, consultant for the Corn Illustrated project, used the example of this year's high-yield plot to make the case that planting date can be an important factor. Using percentage loss per day factors that many agronomists apply, reportedly based on reams of research data over time, he calculated that the delay in planting alone, vs. planting in the May 1 to May 10 time frame, could have accounted for 30 to 35 bushels per acre. That would move the top yield in '08 back up toward the level found in '09, when the high-yield field was planted on time.

Nanda insists that early planting is a key factor to producing high yields. It gives the plant more time to capture sunlight and turn it into stored carbohydrates, which wind up in the grain and become yield. What the key time to plant is on the calendar will vary form region to region, depending upon what latitude you sit at in the Corn Belt.

Balance those findings against a recent look at how well late-planted corn fared in many cases in '08. In Indiana, for example, late flooding meant lots of replanting. Corn was also planted into June in parts of Iowa, Illinois and in Missouri. Yet yields turned out better than expected, contributing ot another large national corn crop. When the devastating flooding was occurring across the Midwest in early and mid-June, it appeared that the crop would be undersized. That's likely one of the factors that contributed to the short-lived, historic rise in corn prices that reached $7 per bushel in late June and in the first days of July, but then quickly retreated.

Bob Nielsen, Purdue University Extension specialist and a corn specialist, originally hailing form Nebraska, says that what unfolded in parts of the Midwest once corn was replanted or planted late the first time illustrates that planting date isn't the only factor that influences yield. When you get good conditions alter in the season, you can still harvest respectable to even very good yields. Part of it is due to genetic improvements plant breeders have made across the board over the past two decades, he notes.

But part of it boils down to other factors, including cooler than normal weather over wide stretches of the Corn Belt when much of the alter-planted corn was pollinating. A cooler pollination season, compared to above-normal-temperatures is almost always conducive to better yields. And there was also less insect and disease pressure in many areas, he says. Rootworm beetles were scarce in the regions they normally infest at silking time. Japanese beetle numbers were also low. Foliar leaf diseases weren't as prevalent in many areas, especially early in the season. Common rust was a factor in some areas, but it typically causes more true damage to seed corn, yield-wise, than to field corn. Some fields were sprayed with fungicides for common rust.

So does what happened last season mean you ought to back off planting early? No one is saying that. Last season was last season. Learn what you can from it, then move on. Keep the lessons in perspective. What you need to look at is what works best for your farm in your location over time, most agronomists say. That's why five and 10-year farm averages and careful record-keeping are so critical.