A stretch of cold and wet weather has significantly delayed Iowa’s corn planting this year, and the window for optimal yields is shrinking.
Just 9% of the state’s corn crop has been planted, according to a Monday report by the Iowa Department of Agriculture and Land Stewardship. In the past five years, about 42% of corn was planted by now on average. Farmers are about nine days behind schedule.
Corn yields are highest if farmers plant seed during a roughly four-week time period from mid-April to mid-May, according to data collected by Iowa State University Extension and Outreach. That varies based on location in the state. For example, the optimal planting window has already closed in north-central and northeast Iowa.
Yields start to drop precipitously by late May. Corn planted in early June is predicted to reach about 80% of its potential yield. At the end of June, that expectation falls to about 40%.
Early planting this year was first stalled by cool soil temperatures that were the result of an April that averaged about 5 degrees below normal, State Climatologist Justin Glisan said.
“It’ll be in the top 15 coldest Aprils” on record, he said.
Sustained soil temperatures of at least 50 degrees are necessary for corn seed to reliably sprout, but those temperatures have lagged in the 40s for much of the planting season so far. On Sunday, most of the southern half of Iowa was averaging soil temps of about 50 degrees, whereas parts of far northern Iowa were in the low-to-mid 40s, according to Iowa State University data.
Still, many farmers in far northwest Iowa — where April was abnormally dry — took advantage of the lack of rain to start planting.
“We’ve got a least a third of the corn in the ground, and maybe 15 percent of the beans,” said Joel DeJong, an Extension field agronomist based in Le Mars. “I know several producers that are done. I know a few others that, because of cool soil temperatures, haven’t started yet.”
Planting in cooler soil can be risky because the seed has more potential to be affected by insects and plant diseases before it sprouts, DeJong said. Further, research has shown that seedlings can be stunted if their first water has a temperature in the low 40s.
“We hope most people sneak by, but there is an increased risk to planting when it’s cool,” DeJong said.
The spring chill was complicated by persistent rainfall that has limited the opportunity for field work, according to IDALS. From April 11 — the generally accepted first day of potential corn planting — until Sunday, there were about eight days over that three-week period suitable for planting on average across the state. That ranged from about 10 days in northwest Iowa to less than five days in southeast Iowa.
“We have not had very good conditions for planting,” said Meaghan Anderson, an Extension field agronomist for central Iowa. “I saw several folks get started, kind of ease into it Wednesday of last week. I suspect that a bit of the crop got planted Wednesday, Thursday and Friday until we got rain.”
Warmer, dryer days are in the forecast for this weekend, but Anderson said central Iowa farmers need at least a week — maybe up to 10 days — of those conditions to finish planting.
“We still have a good window for the optimum yield potential, and we’re holding onto that at this point, realizing that window is getting shorter,” she said. “As soon as anybody can get in the field, they’re going to start planting, and it’s going to be a mad rush.”
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