Hitting The Sweet Spot

Corn growers face a narrow planting window to avoid yield losses due to delays.

Timely planting leads to even emergence, strong stands and optimum yields, Image by DuPont Pioneer

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Science From the Field highlights DuPont Pioneer’s industry-leading research to help growers find profitable agronomic solutions for their farming operations.

They say there’s ‘a time for every purpose’ and that’s certainly true for planting corn. The optimum planting window for corn typically spans about two weeks and varies by region, but missing it can quickly begin to reduce final yields and profitability.

“The timely planting of full-season hybrids allows the corn crop to take full advantage of the growing season,” says Jeff Mathesius, DuPont Pioneer agronomy research manager for the western U.S. “A review of Pioneer’s planting date studies over 18 seasons shows that corn yields are maximized when planting within a two-week period around the optimum planting date.”

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Mathesius adds that the optimum date in those studies proved to be April 16 for the central Corn Belt and April 30 for the northern Corn Belt. “Yields declined for planting dates following the optimum window and the rate of decline increased as the delay lengthened,” he says.

DELAYS DECREASE YIELD. The graph illustrates the results of the study. In the central Corn Belt yields fell by about 2% with a two-week planting delay and 7% with a four-week delay. In the northern Corn Belt, the penalty for late planting was stiffer--totaling about 4% for a two-week delay and 15% for a four-week delay.

“Timely planting is more critical in the northern Corn Belt because our growing season is shorter, even though we have more hours of sunlight through the day during the season,” says Alan Scott, DuPont Pioneer technical product manager in Del Rapids, South Dakota. “There is a trend for growers to plant earlier and to start planting even ahead of the optimum window to reduce the risk of finishing the job after the optimum period. We can plant too early, but if seedbed conditions allow it, the risk of significant yield loss is less than planting too late.”

“There is a risk of frost or other cold weather stress factors from early planting, but the genetic improvements in modern hybrids have minimized those risks,” adds Mathesius. “Also, new seed treatments reduce early season insect problems such as corn wireworm and black cutworm and diseases like pythium and damping off.”

Researchers at the University of Minnesota have estimated the yield impact of four planting factors--uniform seedling emergence; planting timeliness; correct population; and uniform plant spacing. Planting within the optimum window was found to have a 2 to 5% impact on yield--second to achieving uniform emergence with a 5 to 9% impact. Achieving correct population and uniform plant spacing both trailed with only a 1 to 2% impact on corn yields.

FEWER SUITABLE DAYS. Weather, of course, is the leading cause of corn planting delays and the number of suitable days for planting varies widely from year to year. An analysis of USDA data for the years of 1970 through 2013 shows that in Illinois the number of days suitable for field work in the three week period from April 30 until May 20 ranged from as few as 4 to as many as 19 days.

“On average, slightly more than half (11.5) of the days in this three-week period were suitable for field work,” says Mathesius. “Growers need to have enough planter capacity in terms of machinery and labor to get the job done in that time period to avoid yield loss.”

The pressure to plant on time is heightened by indications that the number of suitable days in the spring is slowly declining. In a USDA funded Useful-To-Usable project--designed to transform climate variability data into usable management information--researchers from nine universities confirmed the trend toward fewer days suitable for fieldwork in the planting season. In contrast, the group found the number of suitable days was increasing during the harvest season.

Mathesius notes that planter size has increased steadily, leading many to believe that the U.S. corn crop can be planted more quickly, but that doesn’t prove to be true. “Farm size has increased as well, so the net effect is that although the U.S. corn crop is planted much earlier now than 30 years ago, the pace at which the crop is planted has changed little and weather conditions are the primary factor that determines planting progress.”

“Record corn crops come from maximizing the yield potential of top-yielding hybrids and this comes from planting the fullest season (longest maturity) hybrid possible and planting it on time in good seedbed conditions,” says Scott. “In the northern Corn Belt we see a 1.5 to 2.5 bushel per acre yield advantage per point in the CRM rating (comparative relative maturity). Planting a hybrid with a 100-day CRM rating would have a potential yield advantage of 7.5 to 12 bushels per acre compared to a hybrid with a 95-day rating. Of course, the longer-maturity hybrid could have a higher grain moisture content at harvest--perhaps 2 to 2 ½ points--but at today’s energy prices it would still be money ahead even after drying."

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