July 16, 2008

 

US corn may exceed yields, if growing season is long enough

The 2008 US corn crop already battered by Midwest floods and delayed plantings, still has a "very good" chance of exceeding historic trendline yields, according to experts from Iowa.

 

Speaking Monday (July 14, 2008) during an extension service radio program, the experts said that the key lies in the ability of the corn crop to avoid temperature extremes during the remainder of this rain-shortened growing season.

 

Iowa State University extension climatologist Elwynn Taylor said yields could be above average at just over 150 bushels an acre, compared with the USDA's most recent yield forecast of 148.4 bushels.

 

Although Iowa corn currently averages just 49 inches tall (17 inches below the five-year average), ISU extension corn specialist Roger Elmore said the state's crop has undergone "a major transformation over the past week," achieving a healthy green color as temperatures rise, growth accelerates and "roots get down to where they need to be."

 

Elmore said computer models suggest that Iowa corn will begin silking - which represents the onset of the yield-sensitive reproductive phase of corn plant development - between now and July 27. He calculates that although silking is beginning "probably a week to 10 days behind normal," the corn crop still retains 97 percent of its normal yield potential, "if weather is perfect from here on out."

 

Taylor said near-term weather patterns appear "semi-favorable" for corn pollination. Rains could be normal or a little less than normal in the rest of July and perhaps August, adding that outlooks also favor warmer-than-usual temperatures during the last half of July.

 

Although heat and moisture stress at pollination can produce severe yield losses, Elmore claims the "length of the growing season is really the critical factor."

 

Elmore said ISU computer models show that extremely late planted corn can be expected to yield about 60 percent of a normal yield.

 

Almost half of Iowa's corn crop would qualify as 'extremely late-planted' this season, seeded between mid-June and early July.

 

Agronomists have determined that corn requires about 60 days to reach full maturity after the time it starts to silk, meaning 87 percent of the 2008 crop will ripen sometime after mid-September, versus the five-year average of 64 percent.

 

"We really need to have a late frost," said Elmore. "That will make or break the crop."