University of Illinois

No. 2/April 4, 1997

Is It Time to Plant Corn?

Many farmers who elected not to plant corn before mid-April last year ended up wishing that they had done so, as wet weather later in April and in May kept many out of the field for weeks. With mild weather and good drying conditions in late March and early April resulting in soils' being fit to plant in some areas again this year, many face the same decision once again.

Although I emphasize that it is never appropriate to "mud in" corn in April, some farmers who have tried planting as early in the month as conditions permit have become less cautious over the years, and now start to plant in early April without giving much thought to the wisdom of doing so. Still, a majority of farmers consider soil temperatures too cool for good emergence; and, given the chances for freezing later on, they see early April as a risky time to plant corn. We do not have good figures on how much of the corn planted in early April needs to be replanted, in comparison with that planted later, but the fact that many farmers plant in early April suggests that the percent of acres requiring replant must not be large.

The data we have on effect of planting date on yield shows that we should not expect a yield increase when corn is planted very early. In fact, corn planted April 10 would be expected to yield about 5% or 6% less than that planted the last week of April, when both are at the same plant population. We're not sure why that happens; but early planted corn tends to be slightly shorter than later-planted corn, and there may be some effects of temperature at the time the ear is initiated that affect ear size. The driving factors for many who do plant early is to cover a lot of acres, to finish on time, and to reduce the chances of getting caught by wet weather and ending up planting late.

Many people resist planting early simply because the soils are too cool for emergence, or there is anticipation that soils will cool down again after planting, resulting in a very long time to emergence, lower emergence percent, or freeze injury to small plants. All these risks are real and are greater as one moves from south to north in Illinois. Soil temperature is generally taken, for planting purposes, 2 inches deep at about 7 a.m. (when soil temperatures are generally at their lowest for the day). Although some people take the temperature and decide not to plant if it's below 50 degrees F (the threshold temperature for germination), others disregard this reading and make their decision only on the anticipation of what soil temperature will do after planting. The expectation is that soil temperatures will rise in April, so the approach of anticipating temperatures over the next weeks may be preferable, even if soil temperatures don't quite meet the minimum on a particular day. That is, the decision of whether or not to plant early becomes one based on one's approach to risk. Although we don't have good numbers to assess the risks of planting the first half of April, recent experience would tend to show that such risk might not be as great with modern hybrids, planters, and herbicides as it was years ago.

So, do we plant in early or mid-April if conditions permit? Probably, with caution, but only (1) after completing other field operations; (2) using fuller-season hybrids first with good emergence scores; (3) in the higher, drier fields first; (4) planting carefully with regard to depth control--1.5 to 1.75 inches deep; and (5) using dropped populations of 30,000 or more on productive fields.

Emerson D. Nafziger, Department of Crop Sciences, (217)333-4424