By Roger Elmore, Department of Agronomy
Four-inch soil temperatures passed the 50 degrees Fahrenheit mark in the past few days, air temperatures broke 80 degrees Fahrenheit over the weekend, soil moisture conditions in many areas are good, and the sun is shining. Because of this, I am receiving many questions on whether we should start planting corn. Rain is expected by mid-week across much of the state and air temperatures may drop below freezing by this next weekend. This calls for a caution flag.
While our current planting date data identifies the best time frames to start planting begin this week for the three Iowa regions and end at varying times, there is more to consider.
Corn seed absorbs 30 to 35 percent of its weight in water during germination. Soil temperatures have little effect on this process. However, the time required for radicle emergence is tied to temperature; it increases linearly if soil temperatures are between 46 and 90 F. Little, if any, mesocotyl or coleoptile growth occurs in soils cooler than 60 F. A constant soil temperature of 86 F optimizes seed germination and seedling emergence.
Once the seed begins to germinate, a significant change in soil temperature can cause problems. Research shows that a swing of soil temperatures of 27 F (soil high temperature-soil low temperature) will affect mesocotyl growth. It is possible that corn planted this week will experience this range of temperatures. Seed placed into the ground, yet not emerged, can be injured from a cold period. The drop in soil temperature can cause erratic and uneven stands as it did across the state in 2006, resulting in crop development that varied up to two developmental stages between plants in the same row. Seedlings can also have stunted and distorted leaves or may not emerge from the soil.
Given the current conditions and the forecast for cool-wet weather, the best place for seed this week is probably in the bag.
For more information, please see "Early season cold stress" by Elmore and Lori Abendroth.
Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. Elmore can be contacted by email at firstname.lastname@example.org or (515) 294-6655.