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Issue No. 3, Article 9/April 22, 2011

Corn Planting: Optimism on Hold

After a good start to corn planting, with 4% of the Illinois corn crop planted by April 10, we added only 5 percentage points between April 10 and 17. Most of the crop that is planted is in western and southwestern Illinois. While there was some planting in some places early this week, most fields are wet or very wet on April 20, and the cool temperatures and predictions for more rain promise to slow drying rates for the next week or so.

In 2009, we had time to muster up many devices and distractions to deal with weather delays in planting; we won't try to add to those this time. We certainly needed such distractions in 2009: only 5% of the corn crop was planted by May 5 that year, and it was after May 20 when we reached 50% planted. But beyond anyone's most optimistic dreams, we also had good yields in 2009 (averaging 174 bushels statewide), due mostly to the long, cool growing season. While 2011 could prove similar, most people would consider that a long shot at best.

Almost by definition, data from planting date studies are highly variable, so picking through them takes some art as well as science. Given the truly unpredictable nature of planting date effects for a given year, it's clear that any set of numbers we use is more descriptive of past trials than predictive for the coming season. Still, we believe that these numbers can help us think about what's coming, and if nothing else they can help keep us optimistic that "all is not lost" if it's May before we can plant.

Despite two very different years, response to planting date in Illinois trials in 2009 and 2010 provided averages that are comparable to those we've reported before. In northern and central Illinois, corn planted April 20 to 25 yielded 3 to 5 bushels more than that planted the first week of April. This is consistent with earlier observations that corn planted very early tends to yield a little less than corn planted later in April. Our first planting date this year was in late March at three of our locations. All emerged in 10 to 14 days, but the cool weather has nearly stopped growth for now. We don't think this is doing permanent damage to the plants, but any advantage of very early planting is certainly being diminished by low accumulations of growing degree days. It's also possible that there are negative physiological effects when small corn plants stop growing due to low temperatures. But the decision to plant early under good conditions this year was a rational one, and it should not be viewed as a mistake.

In our trials over the past two years, corn in southern Illinois showed a greater advantage from early planting than did corn in central or northern Illinois. Unfortunately, rainfall patterns and soil in southern Illinois often prevent early planting, and that is certainly true in most places this year. In central and northern Illinois, we found that yields dropped by about 0.6 bushel per day as planting was delayed from about April 23 to May 12, and by about 0.8 bushel per day from May 12 to May 29. Previous work had indicated a little less loss in this earlier period and a little more loss in the later period, but it's safe to assume that yield loss accelerates with delays in planting, from less than half a bushel per day from late April into early May to more than a bushel per day in the last third of May.

Even though we can start to see mounting losses if planting is delayed into May, we need to restrain ourselves from adding to yield losses by planting in poor conditions before the soil is ready. Fields in some cases are worked finer than we consider ideal, and they are not going to dry as fast as they might have with less tillage. Whether we work such fields again before planting will depend a great deal on how fast soil dries, but the decision should not be based on desperation to get started planting. The practice of "opening up" soils with tillage to help them dry out faster is usually not a good one in most Illinois soils, though it is practiced in some of the claypan areas, in part to try to plant early enough that roots can get through the claypan before it becomes impenetrable. Doing this in heavier soils has the potential to produce a disaster, either forming clods that are almost impossible to break down or increasing the tendency of the soil to crust as it dries following another rain.

Almost without exception, opening up a wet soil by tillage means doing a lot of subsurface compaction, and depending on the year this may be a serious problem for the crop's root system. We have no formula for how much more yield might be lost by rushing planting than might be lost by waiting to plant until conditions are better, but it's likely that the tradeoff does not favor earlier planting into poor conditions before late May or early June.--Emerson Nafziger

Emerson Nafziger

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