A spell of cold, wet weather has significantly delayed Iowa corn planting this year, and the window for optimal yields is narrowing.
Only 9% of the state’s corn crop has been planted, according to a report released Monday by the Iowa Department of Agriculture and Land Stewardship. Over the past five years, about 42% of corn has been planted on average. Farmers are about nine days late.
Corn yields are highest if farmers plant seed for a period of about four weeks, from mid-April to mid-May, according to data collected by Iowa State University Extension and Outreach. This varies depending on location in the state. For example, the optimal planting window has already closed in north central and northeast Iowa.
Yields begin to drop precipitously at the end of May. Maize sown in early June should reach about 80% of its potential yield. At the end of June, this expectation drops to around 40%.
This year’s early plantings were initially stalled by cool soil temperatures that resulted from an April that averaged about 5 degrees below normal, the state climatologist said. Justin Glishan.
“It will be in the top 15 coldest Aprils” on record, he said.
Sustained soil temperatures of at least 50 degrees are needed for corn seeds to germinate reliably, but these temperatures have so far lagged in the 40s for much of the planting season. As of Sunday, most of the southern half of Iowa had an average ground temperature of around 50 degrees, while parts of far northern Iowa were in the 40s, according to data from the ‘Iowa State University.
Still, many farmers in far northwest Iowa — where April was unusually dry — took advantage of the lack of rain to start planting.
“We have at least a third of the corn in the ground and maybe 15% of the beans,” said Joel DeJong, a Mars-based Extension field agronomist. “I know several producers who are done. I know of a few others who, due to cool ground temperatures, have not started yet.
Planting in cooler soil can be risky because the seed has more potential to be affected by insects and plant diseases before germinating, DeJong said. Additionally, research has shown that seedlings can be stunted if their first water has a temperature within 40 degrees.
“We hope most people will pass by quietly, but there is an increased risk of crashing when it’s cool,” DeJong said.
The spring cold was complicated by persistent rains which limited opportunities 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 in that three-week window that were suitable for planting on average across the state. This ranged from about 10 days in northwestern Iowa to less than five days in southeastern Iowa.
“We haven’t had great planting conditions,” said Meaghan Anderson, extension field agronomist for central Iowa. “I saw several people kicking off, sort of getting comfortable on Wednesday of last week. I suspect part of the crop was planted on Wednesday, Thursday and Friday until we had rain.
Warmer and drier days are forecast for this weekend, but Anderson said farmers in central Iowa need at least a week — possibly up to 10 days — of those conditions to finish planting.
“We still have a good window for peak return potential, and we’re sticking with it at this point, realizing that window is getting shorter,” she said. “As soon as someone can get into the field, they’ll start planting, and it’s going to be a wild ride.”
Low soil temperatures, soggy conditions slow spring corn planting