Potential for good yield still there but rain needed
By Jean Caspers-Simmet
Date Modified: 08/02/2012 2:06 PM
KANAWHA, Iowa —While potential still exists for good yields, searing heat and scant moisture will soon start taking a toll on the corn crop, farmers learned at last week's field day at Iowa State University's Northern Research Farm at Kanawha.
"We could still end up with a year like 2009, which was the best yield ever, and we could end up with a disastrous yield like 1988." said Roger Elmore, Iowa State University Extension corn production specialist. "We have a ways to go before that's determined."
Elmore said farmers need "spoon feeding rains" every three to four days unless they get a storm to fill up the soil profile. Unfortunately, that kind of widespread rain doesn't look likely in the short-term.
"If you look at the percent of Iowa subsoil that is short or very short of moisture, you see that we don't have a lot of reserve," Elmore said. "We went into spring without a reserve, and we're not storing any. We need at least an inch of rain every two to four days."
The June 26 U.S. Drought Monitor report showed 71 percent of the Midwest in abnormally dry to early stages of drought.
David Rueber, research farm superintendent, said the year started dry but moisture soaked into the ground thanks to a warm winter. March was the warmest on record for the research farm. Rueber has records going back 40 years.
"Not only was it the warmest March, it was warmer than the average April temperature," Rueber said. "The ground thawed March 8, and 1.5 inches of rain soaked in."
April continued the warm trend with an average temperature of 51.9 degrees vs. 48.9 degrees for normal. The research farm received 4.25 inches of rain in April vs. the normal 3 2/3 inches. May was also warmer, averaging 64.9 degrees compared to 60.7 for normal. May received 3.13 inches of rain vs. the normal 4 1/3 inches.
For June, rainfall was 1 2/3 inches compared to 4 1/4 for normal, Rueber said.
The 106-day hybrids planted the end of April should be silking by next week.
There are many components of yield, Elmore said. It starts at planting with proper plant population and a uniform stand. Corn plants two leaves or more behind other plants in a stand can significantly reduce yield if there are enough of them.
This spring 41 percent of farmers planted corn the fourth week in April in what they thought were perfect conditions, but the weather turned cold and wet for several weeks, Elmore said. There were emergence issues, uneven stands, rootless corn, and compaction and sidewall compaction took a toll.Corn plants which intercept the most possible light at silking will have improved yield, Elmore said. Anything that reduces leaf area before silking will reduce yield potential.
Plant stress causes low plant growth rates and delayed silking which spreads out the time between pollen shed and silking."You want pollen shed and silking to be as close together as possible," Elmore said. "With stress these widen out and you end up with kernels on the ear tip that don't fill. Grain yield is particularly sensitive to stress conditions during a time bracketing silking."
Stress around silking reduces yield, Elmore said. Increased photosynthesis at silking increases kernel numbers.
"A stress-free environment decreases the time between pollen shed and silking, which in turn brings more kernels per plant and ultimately more yield," Elmore said.