New corn recommendations apply to Iowa growers

CLARION, Iowa — New Iowa State University planting date recommendations divide the state into three regions rather than giving one statewide guideline.

Tthe recommendations offer an earlier and shorter window for optimum yields for north central and northeast Iowa.

Lori Abendroth, associate corn agronomist at ISU, outlined the new recommendations during the recent North Central Iowa Research Association annual meeting at the Heartland Museum in Clarion. The research association owns ISU’s Northern Research Farm at Kanawha.

Abendroth, who works with Extension corn specialist Roger Elmore, said the old recommendations were based on research from the 1990s. She, Elmore and two statisticians wanted to know if recommendations are different today.

Nationally and in Iowa the planting date has been moving 0.3 to 0.8 days per year earlier over the past 30 years.


"We’re planting a half day earlier per year," Abendroth said. "In Iowa we’re beginning planting 13 days earlier than in 1979."

Many reasons exist for the change — larger equipment, more stress-tolerant hybrids, improved seed treatments, reduced tillage systems and increased farm size.

"Research shows there is less yield loss from planting early than late so if you’re going to be outside the optimum planting window, it is generally better to go early than late," Abendroth said.

In developing the new recommendations, researchers used three years of data (2006, 2007 and 2009) from six locations in Iowa — Kanawha, Nashua, Sutherland, Ames, Crawfordsville and Atlantic. The research was done during 2008, but wet weather prevented timely planting, and the data wasn't used. Five planting dates were used at each site.

Researchers tried to start as close to April 1 as possible and then adjusted the intervals to end on May 31. Recommendations were developed based on maximum yield.

Research showed that results from Kanawha and Nashua followed a slope that was fairly flat at the beginning and then it dropped off much more significantly than the other locations.

Northwest Iowa receives more growing degree days and so it is grouped with central Iowa recommendations. The third recommendation is for southern Iowa.

"Our research showed a more significant drop yield with later planting in north central and northeast Iowa," Abendroth said. "That hasn’t shown up in the research before. You have known it to be true. We think this is due to a tighter length of growing season. When we’re late we just don’t have the heat and light accumulation that is necessary to contribute to yield."


The best day for planting corn in north central and northeast Iowa is April 17, but since most farmers can’t finish planting corn in one day, researchers defined windows of time for 95 percent to 100 percent of yield. For north central and northeast Iowa that is April 12 to May 2 with 98 to 100 percent of yield in the April 12 to April 30 window. The window for central and northwest Iowa is April 15 to May 18 and in southern Iowa, it is April 11 to May 13.

"With the new recommendations, the window has moved up," Abendroth said.

New book to detail how a corn plant grows and develops

The book, "Corn Growth and Development," which will be available within a couple of weeks.

The book replaces the long-time standard, "How a Corn Plant Develops."

Iowa State University associate agronomist Lori Abendroth, who took the lead in writing the book, said she has great respect for the 1966 book and its author, John Hanway.

"The old book was based on older hybrids and research," Abendroth said. "We’ve updated it and included a lot of new information and research."

The new book is twice as long, and it includes whole plant images — roots below ground and above ground plants in various developmental stages. It backs up all statements with other research.


The book clarifies corn plant staging methodologies and offers conversion factors. It offers predictions of plant and ear development based on accumulated growing degree days and descriptions of root development. It provides a description of ear and kernel growth, current dry matter and nutrient accumulation data from emergence to maturity.

A corn plant provides 20,000 pounds of biomass per acre — half as grain and half as leaf and stalk, Abendroth said. A 225-bushel per acre corn crop pulls 190 to 200 pounds of elemental nitrogen, 35 to 36 pounds of phosphorus and 120 to 135 pounds of potassium from the soil.

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