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Thinking About Planting Conditions

April 19, 2002
A roundabout trip from Champaign to the Quad Cities and back on April 16 showed a large number of fields that looked dry across the top, some of which were being worked (including some spraying in 30-mile-per-hour wind, but that's another topic). Perhaps 1 percent or so of the fields were being, or had been, planted. It is clear that memories of daytime high temperatures in the 40s and 50s are quickly set aside and that it takes only about 2 days of temperatures in the 80s to get people planting. Without doubt, only 2 days of high temperatures do a lot to bring soil temperatures up. They are probably in the 50s at the depth of seeding in most Illinois fields now. And along with this temperature increase comes a large increase in the rate of drying. That's especially true when the wind blows. Surface soil moisture has dropped rapidly.

Most of the fields that had been planted looked like they were in fair to good shape for planting. There were some exceptions. The cloddiness at the surface generally indicates that the field was worked when the moisture content of the surface soil was too high. It is likely that some fields that looked better on the surface were worked and planted when the subsurface soil layers were wetter than they should have been. Many of those who want or need to start planting early have learned to set tillage depth and speed to leave a good surface for planting, but at the same time such fields usually have considerable subsurface compaction that could be a detriment to root growth and moisture extraction later, when the plants need it.

On the other hand, there were, as usual, more "powdered sugar" fields--those where the surface has been thoroughly pulverized--than we hope to see. I expect that many of these fields were tilled in the fall with an implement that left them almost ready to plant and then were tilled again in the spring, perhaps even twice. The winter provided enough freezing and thawing to leave surface soils reasonably well granulated. Though tilling twice or more often in the spring probably wastes the cost of at least one trip over the field, emergence should be fine in these fields unless we experience heavy rains, especially if the rains are followed by a period of cool weather. Crusting could take a toll in such fields, but an equal danger is that wet soils with poor structure tend to have very little stored air and seeds or seedling can die quickly from lack of oxygen, often followed by attack of diseases. "Overworked" fields also tend to have planting depth deeper than the planter setting indicates, which can lead to slower emergence and even more problems during germination and emergence.

In general, we should be making a seedbed that leaves the planter to do what it was designed to do--break clods next to the seed furrow, firm the soil around the seed such that seed-soil contact is good, and to place seed at uniform depth. Modern planters have been engineered to do this. Compared to the opener shoes and concave presswheels used 30 or more years ago, planters today do a vastly better job of placing and covering seed. We need to do any tillage with this in mind: leave something for the planter to do. Otherwise, we can easily end up with seed in less than ideal conditions to foster rapid emergence.

Corn that we planted here at Urbana on April 5 started spiking through on April 16, and we will be monitoring its emergence on a daily basis. This trial includes some of the polymer-coated seed that I mentioned several weeks ago, and so we will be able to tell how much the coating delays emergence. Of course, the unusually rapid rise in soil temperatures this week will mean that this trial is not very "typical." But few such trials ever are "typical," or at least not "average." These two terms are not really the same. "Typical" is a range, and "average" is a single point within that range. It's useful to keep this difference in mind as we tackle crop production problems, especially those related to weather.--Emerson Nafziger

Author: Emerson Nafziger

The Pest Management and Crop Development Bulletin
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