Planting Corn--How Early Is Too Early?

March 17, 2000
A relatively dry winter and some very warm temperatures in early March had a lot of people thinking about planting corn; and there are reports that some corn was planted in Illinois during the first week of March. While most would consider that "just too early," others point out that planting in (late) March worked well last year, and that, if the unusually warm and dry conditions persist, the crop should do well. Soil temperatures were above 50°F in many parts of Illinois by early in the week of March 5, and this added to the "indicators" that it might be time to think about getting started.

The return to seasonably cool weather and some snowfall over the last weekend have cooled the early-planting urge for now. Cool soil temperatures have greatly slowed the uptake of water into the corn seed that has been planted, and it is likely that most of the planted seed has not had time to take up enough water to germinate. Water uptake will continue slowly, but soil temperatures will need to rise above 48°F or so for the actual growth of the seedling to begin. The seed is not harmed by this slowdown, but once the radicle (first root) breaks the seedcoat, then the interior of the seed is open to attack by microorganisms, after which it's a race to see whether the seedling will emerge before the seed is rotted out. If soil temperatures remain below 50°F for more than 2 weeks or so after the seed takes up water, then chances increase that the microbes will win the race. If temperatures remain average for the next week or two, then the seed planted early is likely to have emergence problems.

Aside from the understood risk that planting in March brings to the health of the seed and seedling, there is the question of how the crop might respond to such early planting in the event that it does emerge well. Again, we tend to remember our most recent experience (1999) in which early-planted corn did very well, with warm April and May weather and so few interruptions to growth once the crop emerged. This year could be similar once we get past the cool temperatures at present--the dry pattern that has held over much of the Midwest continues, and that usually means warmer-than-average temperatures. But then again, April could turn wet and cool. From work done some years ago, we determined that corn planted in early April often yields slightly less than that planted in late April, even when stands are identical. We think this is physiological, perhaps tied to the fact that temperatures are cooler during critical stages of ear development, and also to the fact that leaves that form early tend to be slightly smaller due to lower temperatures during their formation.

So what's the bottom line on very early planting? It will likely be done by some adventurous producers as soon as soil conditions allow each spring, with results likely to be mixed, depending on the weather pattern after planting. Though some think we're in a long-term cycle of warming, odds still favor a return to lower temperatures after planting if planting is done during warm weather in March. If such cooling is not accompanied by rainfall, then the seeds will survive for weeks until temperatures rise and the plants can emerge. If it gets wet, though, replanting of a lot of very-early-planted corn will likely be necessary. And we should not expect that corn planted very early will yield more than that planted in late April. Of course, if wet weather sets in during April and planting cannot resume until well into May, then the planting delay could cost more yield than we might lose from very early planting.

One thing we really do need to avoid is planting in March or early April when soils are too wet to till or to plant without doing soil compaction. First, there is a reasonable expectation that, when soils have already been dry enough to plant, they will dry out reasonably well following April rainfall. Second, seed planted into wet, cool soils often emerges poorly, particularly if the surface dries out and a crust forms. Finally, our goal should be to finish planting by late April or early May, and most people are equipped to do that even if planting doesn't start until mid- or even late April.

A final note: corn that is planted very early and that does not produce an adequate stand can often be replanted in a timely manner. This means extra expense when it's needed, but it does lessen the risk associated with very early planting. There are other potential problems with very early planting, such as expected longevity of herbicides and insecticides, but with lots of acres to plant, some producers will continue to take the risk.--Emerson Nafziger

Author: Emerson Nafziger