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Now Is It Time to Plant?

09 April 2012

US - Almost nothing about the spring of 2012 in Illinois has been normal so far, writes Emerson Nafziger, University of Illinois Extension Specialist, Department of Crop Sciences.

Rainfall totals were below average over nearly the entire state, and in many places temperatures have broken records on an unpredecented number of days. According to the Illinois Weather & Crops report issued by the Illinois office of the National Agricultural Statistics Service, an astounding 5 percent of the Illinois corn crop was planted by April 1, and 1 percent was planted by March 25.

The first April reports (issued on Mondays with estimates as of the previous day) show that in only two of the past 20 years--2003 and 2004--was any corn reported as planted by the first Sunday in April, and in both of those years it was 1 percent. In a few other years of dry weather in early April the report stated that farmers were "anxious to start planting," but it is clear that almost no one back in the 1990s and before thought that planting that early was a good thing.

It remains dry in most of Illinois in the middle of the first week of April, and while planting is getting a serious start in some areas, in others farmers are still waiting until the crop insurance date at the end of this week, or until after Easter. One good reason for waiting until the second week of April to start planting is that the weather forecasts--particularly models of temperatures over the next 7 to 10 days--will be updated, taking us past the middle of the month. While we all know that forecasts can change suddenly in any direction, as the middle of the month approaches we get a clearer idea of whether the emerged crop is in trouble.

The largest cause of concern is the possibility of frost that would kill or badly damage the emerged crop. According to 30-year weather data summarized by the Midwest Regional Climate Center, the median dates at which temperatures of 32 degrees last occur in the spring are April 28 at Rochelle (northern Illinois), April 15 at Urbana (central Illinois), and April 12 at Mt. Vernon (southern Illinois). Ninety percent of the time that temperature is last reached by May 14 at Rochelle and by April 30 at both Urbana and Mt. Vernon--meaning that 1 year out of 10 it is reached later than those dates. The earliest that the last freeze date was reached was in March at all of three of those locations. So if you are inclined to optimistm and figure that the pattern we've had so far this spring will hold, you might not lose too much sleep over concern that the emerged crop will freeze.

With temperatures continuing to stay well above normal, the crop continues to emerge rapidly. The small plot we planted at Urbana on March 16 has reached the 2-leaf stage (V2), and stands and crop appearance are very good. That crop has received about 275 growing degree days (GDD) since planting, so growth is tracking well with GDD.

There are indications that temperatures are dropping back some over the next week, meaning that GDD accumulations will return to more normal levels. Accumulation for March has averaged 67 GDD over the past 10 years at Urbana; in 2012 it was 233, about 50 percent higher than in any of the previous years. Average accumulation in April and May have been 166 and 374. That means that corn planted on April 1 in a normal year will not grow as much by May 1 as the corn planted in mid-March grew by April 1 this year. So a return to more normal temperatures will certainly slow growth, but the effects of warm temperatures up to now will not disappear.

Soil temperatures remain above average, but with the soils as dry as they are now, daily fluctuations are relatively large--the water in soil holds heat better than the mineral material or air. If night temperatures should fall into the 30s, the warm soil will serve as a heat source, helping to protect the leaves from frost damage by radiating to them even as the leaves radiate to the sky. This won't help for very long if temperatures drop to freezing or below, but it could be a factor.

Now that it's April, is there any reason to wait much longer to start planting? I recently updated planting date data to use responses from the last 5 years; the data are from four central and northern Illinois locations, but responses were so similar that I averaged them. Based on the line (see below), planting on April 20 produced the highest yield (201 bu/acre) and planting on April 30, May 10, May 20, and May 30 yielded about 2, 7, 15, and 27 bushels less than the highest yield, respectively. If this year follows the same pattern, planting on April 1 or April 10 will yield 7 and 2 bushels less than planting on April 20. These responses are not greatly different than we have seen before, but as always it's worth bearing in mind that few years come out just like the average.

Corn planting date response, averaged over four Illinois sites and 5 years (2007–2011).

About the only agronomic issue at this point, besides the ongoing concern about whether the weather pattern will change for the worse, is whether there is enough soil moisture to allow seeds to germinate. This is especially true in fields where soils were tilled some time ago and where, without rain, drying of the surface soil has continued. Whether to plant into dry soil with the idea that seeds will germinate quickly once it rains is not an uncommon issue in late May with soybeans, but not in early April with corn. Corn seed needs to take up less water than soybean seed to emerge, and as long as soils stay relatively dry, corn seeds tend to stay viable even if it's too cool or too dry for emergence.

It's probably not a good idea to till again to try to bring up moisture; that often results in uneven distribution of soil moisture down the row, causing unevenemergence, which can reduce yields. Soils in most tilled fields are fairly fine by now, even after only one tillage pass, and more tillage would both lead to more soil moisture loss and add to the risk of crust formation after heavy rain.

So it looks like planting the corn crop is on course to be the earliest ever in 2012, providing the weather pattern now in place continues to hold. Our most serious concerns--those related to deterioration of weather conditions--diminish with each day now, and we expect planting to accelerate quickly over the next week. With luck, including getting rain at some point in the coming weeks, the crop will be off to a good start.

In the next issue of the Bulletin I'll address the issue of soybean planting date and soybean management. For now, the focus should be on getting corn planted first. But our recent data show good yields from planting soybeans in April, and so as long as we can get them planted under good conditions, there's little need to wait until May to start to plant.

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