May 7, 2013
The extraordinary drought of 2012 is now being followed up by an unusual spring of 2013. Recent rains have helped, but the drought continues and many areas of the state still have severely depleted subsoil moisture levels. In addition, recent temperature swings may have affected crops planted in the last week or two.
While there is some debate over exactly what temperatures cause imbibitional chilling and what timing is associated with the response, there is undoubtedly a response from corn plants that imbibe cold water in the first 48 hours after planting. With the recent cold weather and fields being planted to "beat" the rain, there is a chance that some early planted fields may experience symptoms of imbibitional chilling.
It is generally recommended that soil temperatures be 50-55°F before planting corn to prevent this from happening. (View daily updates of soil temperatures on CropWatch.) As of May 1, we measured soil temperatures at 42°F at 8:30 a.m. Some reports have suggested that corn will not be injured at soil temperatures above 41°F, however there is certainly some risk of injury from imbibitional chilling. It is recommended that planting be delayed until soil temperatures are higher (high 40s) with forecasts of longer term warm weather to ensure that the seedlings are more successful.
When corn seeds imbibe water, the cell membranes will stretch and cells will expand. When a damaged cell membrane is rehydrated, it may not return to its normal shape and size. This can create a "leaky" cell. Water is at its densest at about 39°F so when cold water is imbibed, it may result in additional membrane damage. These ruptured membranes may occur in the cell walls and in the mitochondria. In a phone discussion with Joseph Burris, seed physiologist at the Iowa State University Seed Testing Laboratory for 31 years, he described the action as being much like what happens with a damaged fishing net. When the net is fully expanded, more things will pass through the damaged holes.
In the plant this action may somewhat disrupt the embryo/endosperm enzymatic conversion to energy, but mostly results in leakage of cell solutes and sugars. This, in turn, is likely to reduce growth rate and interfere with normal regulation and growth of the emerging seedling.
Some inbred lines (seed parents) are clearly more susceptible, and the seed industry has been actively eliminating the most sensitive ones from use. However, if environmental conditions are extreme, many fairly tolerant parents may still show damage—it is a physical phenomenon that can override biology.
If you have early planted corn, it will be important to scout it early. Poor stands may need to be replanted.
Extension Cropping Systems Specialist, West Central REC