University of Illinois

No. 6/May 2, 1997

Early Planted Corn Starting to Emerge

Corn planted anytime during the first 20 days or so of April is now starting to emerge, after what in some cases has been almost a month of very slow germination. The corn that we planted on the South Farm had coleoptile tips just beneath the soil surface this morning (April 30) and should emerge during the day today. There were not many warm days during the time corn seed was in the soil, but it appears that the relatively dry conditions during this period helped the seeds and seedlings to come through their "dormancy" quite well. We do not really know whether the seed continues to use up stored carbohydrates when soil temperatures are too low, or whether biochemical activities simply slow to very low rates. In any event, there does not seem to be much need to replant, though we have had a few reports of this being done.

One rather obvious effect of the cool soils during April will be considerable synchronization of the growth of corn planted on different dates. With warmer temperatures, plantings spread over a month's time will emerge within about a week's time. As we have noted before, corn planted in early April tends to yield less than that planted in late April. With emergence delayed for corn planted early, there should be less yield difference of this type this year.

Even though most reports are that the corn crop is emerging well, stand evaluation will be important in many fields. As we have noted before, the measuring wheel method is a quick and accurate method to use. To apply this method, set the measuring wheel to zero and walk along a row, counting plants (by 3s) until you've counted 150 plants. The distance traveled can be converted to plant population by dividing this distance (in feet) into the factor 2,613,600 for 30" rows. For 36" rows, this factor is 2,178,000; for 20" rows, it's 3,920,400; and for 15" rows, 5,227,200.

Another topic of recent concern has been that of plant-to-plant spacing variability. Such variability has usually been measured as the standard deviation (a statistical measurement) of plant spacing. This measurement, which requires measurement of spacing between a lot of plants, is difficult and time consuming. Without discussing this in detail, it appears that plant-spacing variability is less important than plant population. Plant population is in fact related to plant-spacing variability, with lower variability at higher populations, unless the higher populations come mostly from doubles. Under normal circumstances, if plant populations are high enough, I would suggest paying little attention to plant-spacing variability.

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