Later Planting Doesn't Necessarily Mean Lower Corn Yield

Cold, wet weather in early May has further delayed planting, but later planting doesn't always mean lower corn yield.

Published on: May 4, 2013

Go ahead and plant corn or wait until better weather comes next week? That was the question Iowa farmers asked themselves on April 30 and May 1 -- Monday and Tuesday of this week. Many went ahead and planted some corn, even though the weather forecast was for temperatures dropping into the 30 degree F range in central Iowa on May 2 and 3 and staying cold and wet for a few days. That cold and wet weather did indeed arrive along with snow and ice slush over a wide area of the state.

So what's going to happen to the corn seed as it sits in cold, wet soil here in early May, waiting for the weather to warm up next week so corn planting can resume? Would you have been better off leaving your seed in the bag instead of planting it last Monday and Tuesday -- April 29 and April 30? Will your stand be reduced? Will you have to replant?

LATE PLANTING DATES: While the normal recommendation is to plant corn early to maximize yield potential, remember that soil conditions and forecasted weather affect planting recommendations. "Early planting does not ensure high yields just as planting late does not foretell low yields," says Iowa State Extension corn agronomist Roger Elmore.
LATE PLANTING DATES: While the normal recommendation is to plant corn early to maximize yield potential, remember that soil conditions and forecasted weather affect planting recommendations. "Early planting does not ensure high yields just as planting late does not foretell low yields," says Iowa State Extension corn agronomist Roger Elmore.

Iowa State University Extension corn agronomist Roger Elmore and his graduate student Warren Pierson have studied years in the past when Iowa had rain-delayed planting. They provide the following answers and information. Elmore writes the "Corn Source" column each month in Wallaces Farmer magazine.

Recommended planting dates for corn in Iowa range between April 12 and May 18
Average recommended planting dates for corn in Iowa lie between April 12 and May 18 in order to achieve 98% to 100% yield potential, but this varies a bit on the specific location. Iowa soil temperatures are considered good for planting when they are 50 degrees F or higher because that's the temperature necessary for corn seed germination. But the weather forecast wasn't ideal for a corn seed to germinate and begin emergence the week of April 30 to May 6. Highs on May 2 and 3, 2013, were in the low 40s with lows in the mid-30s with rain, sleet and snow.

Every decision that you make influences the size and scope for corn yields. From the corn hybrid you select to the seeding rate and row width you choose. Download our FREE report over Maximizing Your Corn Yield.

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Last year, on April 26, Iowa soil temperatures ranged from 58 to 64 degrees F; however, by April 29 soil temperatures dropped to 49 to 53 degrees F across the state. This swing in temperatures, coupled with rain at that time, resulted in many reports of lower relative yields for corn planted between April 22 to 26 than corn planted later. Fluctuations in soil temperatures are related to deformed mesocotyl growth, which can result in "corkscrewed corn."

According to the USDA/NASS latest weekly survey, which was as of April 28, 2013, approximately 2% of Iowa corn acres were planted by that date. This is somewhat similar to 2011: by April 24, only 3% was planted and, by May 1, only 8% was planted. Within two weeks after that though, approximately 84% of Iowa's corn acres (11.9 million acres) was planted, bringing the total planted to 92%. Even with this later-than- usual planting corn yield was about 3% above trendline in 2011.

Even with later-than-usual planting, yield in 2011 was about 3% above trend
One way to look at yields at different planting dates is to compare state average yields -- as reported in deviations from the trendline -- to the percent of the crop planted at different times during the spring. This is the way Purdue corn agronomist Bob Nielsen ("The Planting Date Conundrum For Corn") and University of Illinois agronomist Emerson Nafziger ("Planting Delays and Corn Prospects") looked at corn yield in their recent articles.

For example, in Iowa the trendline for acres planted by April 30, compared to yield relative to trendline, is actually negative (Figure 1). This suggests that delayed planting tends to increase yield potential although the trend is a weak one. The negative trend for acres planted by April 30 is likely due to the negative effect of 2012 and the three years of near trendline yields with 60% to 70% of Iowa's corn acres planted. What is clear is that earlier planting does not always guarantee high yields, and late planting does not always foretell low yields.

Although the trendline of corn planted by May 15 was positive, three years were exceptional. In 1982, 1984 and 2008 only 45%, 35% and 46% of the crop was planted by May 15, respectively; yields were above trendline by 20%, 7% and 6% respectively (Figure 2). In 1991 and 1995, only 33% and 30% of the crop was planted by May 15, respectively. In these two years in which planting proceeded slowly, yields deviated from trend by only -3% and -6% (Figure 2).

Every decision that you make influences the size and scope for corn yields. From the corn hybrid you select to the seeding rate and row width you choose. Download our FREE report over Maximizing Your Corn Yield.

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The relationship between acres planted by May 30 and yield is not strong; this is likely due to the fact that the majority of corn acres are generally planted by the end of May. In 1982, corn was only 71% planted by May 30 and yields were above trendline by 20%; however, in 1991 and 1995, only 70% and 80% of corn was planted and yields were below trendline by -3% and -6% (Figure 3).

Nielsen found similar trends in Indiana and suggested that farmers be patient and not "mud in" corn. The effects of "mudding in" corn are likely more negative than the effects of a late planting date for corn. Iowa State's Roger Elmore also recommended patience in information he posted online on April 29, 2013.

Iowa farmers are equipped to plant more acres per day than ever before
Having planted 1.2 million acres per day in critical windows of recent years, Iowa farmers are now equipped to plant many acres per day than ever before. Waiting for soil temperatures to rise above 50 degrees F and warmer weather in the forecast is most favorable for corn growth, development and yield. Delaying planting until conditions improve will encourage more uniform and faster emergence, greater emergence percentage and more rapid growth and development. Planting date is only one of many yield factors; weather conditions the rest of the season, management and genetics will likely be more substantial yield factors.

While our normal recommendation, based on multiple years and locations of data, is to plant early to maximize yield potential, keep in mind that soil conditions and forecasted weather affect planting recommendations. Early planting does not ensure high yields just as planting late does not foretell low yields.

Warren Pierson is a graduate research assistant. He can be reached at wpierson@iastate.edu or 515-294-1360. Roger Elmore is a professor of agronomy with research and Extension responsibilities in corn production. He can be contacted by e-mail at relmore@iastate.edu or 515-294-6655.

Every decision that you make influences the size and scope for corn yields. From the corn hybrid you select to the seeding rate and row width you choose. Download our FREE report over Maximizing Your Corn Yield.



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