AMES, Iowa -- Iowa’s corn has experienced an unforgiving growing season. With the last breaths of summer in the air many wonder what it will take to maximize yields from this date forward. According to the recent USDA report, Iowa’s corn is about two weeks behind the five year average.
Eleven percent is ready for a frost, 71 percent is in the dent stage. At beginning dent the crop normally needs about three weeks to mature. The bottom line - regardless of location in Iowa, the corn crop needs a normal or later than normal frost date to maximize yields.
“Recall that planting dates were later than we would like to maximize corn yields, and that early-season growth was hampered by cold and wet soils,” said Roger Elmore, Iowa State University Extension agronomist. “Plant emergence was difficult and slow. Rainfall prevented timely post-emergence operations such as side-dress fertilizer applications and post-emergence herbicide applications.”
The cool temperatures after silking, which happened in 2008, are necessary for maximum yields. Slow heat unit accumulation rates characterize 2008 in Iowa. The disadvantage of this is that slower crop development coupled with later than desired planting dates necessitates a long growing season, and a late frost.
“In late August we suggested that to maximize yields in central Iowa, based on the Ames weather data through Aug. 22, large amounts of sunlight and rainfall after silking were necessary to maximize yields from that point forward,” said Elmore. “Plus we needed a late frost on or after Oct. 22 - to some extent this has happened. The average frost date in Central Iowa is Oct. 17.”
Elmore tested his thinking earlier this week by using a computer model with 2008 weather data through Sep. 15 for Ames. Table 1 shows a summary of the results. (See Table 1 linked below.)
If the weather after Sep. 16 is like the median year for Ames, a crop could yield 91 percent of its normal potential, if there are no other limiting factors. Based on Table 1, a maturity date of Oct. 28 is necessary for the highest yield potential and a frost date later than that.“ This has happened in four of the last 30 years.
In addition to a late frost, plenty of sunlight is necessary to maximize yields. This week’s weather is promising. Iowa’s 2008 corn crop needs a later than normal frost date to maximize yield. Conditions that hasten crop maturity from this point forward or an earlier frost will reduce yield potentials.
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