April 27, 2007

The hard freezes of April 13-16 and the heavy rains of April 24-25 have delayed corn planting for many producers. This article addresses some of the questions producers are likely to face over the next month.

Q. What is the optimum planting date for corn in Nebraska?

A. In Nebraska, on average, it is May 1-May 15. The range is a little earlier in the southeastern and south central parts of the state and a little later in the northeast. Planting in late April can be beneficial for spreading work over more days, but does not necessarily result in a yield benefit. Optimum planting date varies between years. The ideal planting date allows the corn to avoid very hot conditions during pollination and to extend grain fill past the very hot weather of late July and early August. Individuals interested in exploring the effect of different planting dates with different weather conditions should consult UNL's Hybrid-Maize model, available at http://www.hybridmaize.unl.edu.

Q. How much does yield potential decline when corn is planted late?

A. The rule of thumb is 1-2 bu/day past the optimum planting window. Yield potential declines slowly as planting is delayed through mid-May, and accelerates if planting is delayed through late May and early June. In studies across the Midwest, yield potential of corn planted May 19-20 was 94-99% of corn planted by May 5-7.

Q. Is there always a yield penalty for late-planted corn?

A. No. It depends on all the "yield influencing factors" the crop faces that year. Planting date is one factor, but yield potential also depends on heat or available moisture during pollination and grain fill, the timing and magnitude of disease, insect, or weed pressure, nutrient availability, and stand establishment. For example, corn planted April 20 may pollinate during a hot, dry period, whereas corn planted May 15 may catch timely rains and out-yield the earlier planted crop.

Q. When should I consider switching to a shorter-season hybrid?

A. Please refer to the companion article in this week's CropWatch.

Q. What precautions should be taken when planting into wet soil?

A. The best precaution is to wait until the soil is dry enough to avoid side-wall compaction and crusting that will interfere with emergence and root establishment. Please refer to Avoiding Sidewall Compaction at Planting - Don't Plant Too Shallow and Tips to Reduce Sidewall Compaction in the April 20 CropWatch.

Q. Should I change my seeding rate in late-planted fields?

A. There is no reason to change seeding rates for later planted fields. Because soil temperatures will generally be warmer in later-planted fields, germination and emergence should occur sooner and be very uniform. Use the optimum seeding rate for the yield potential of each field.

Q. Can I save time by not applying a starter fertilizer and still maintain high yields?

A. Starter fertilizer provides the greatest benefit when corn is planted into cool soils where germination and seedling development is slow, or when soil tests indicate low phosphorus levels. Later planted fields will generally be warmer and seedling development more rapid. Eliminating starter fertilizer application may allow an operator to plant more acres in a day - an advantage in a spring that is forecast to be relatively wet.

Q. What will happen to soil nitrogen with all the rain?

The heavy rains of the past week likely moved much of the residual nitrate deeper into the soil. Warm, saturated soils provide an ideal environment for denitrification, another source of nitrogen loss. Nitrogen in the form of ammonium should remain near the soil surface. Where nitrogen was applied last fall or earlier this spring, much of that nitrogen will still be available. If nitrogen has not yet been applied, planning to side-dress nitrogen later in the year will enable earlier planting.

Bottom Line

Planting date is only one of many factors that influence yield. We are still within the optimum corn planting window and will be for another three weeks. As Bob Nielson, agronomist at Purdue University, wrote, "Mudding in a crop early to avoid planting late will almost always end up being an unwise decision."

Other references:

• Abendroth, L., R. Elmore. 2007. Corn planting: consider soil temperature and date.
• Elmore, R., L. Abendroth, J. McGuire. 2007. Cold weather dampens corn planting.
• Elmore, R. 2003. Despite delays, don't switch to shorter-season corn yet.
• Nielson, R. 2007. Perspective on Planting Dates & Corn Yield Potential.
• Nielsen, R. J. Obermeyer, T. Vyn. 2003. Delayed Planting Considerations for Corn.

Mark Bernards
Extension Weeds Specialist
Richard Ferguson
Soil Fertility Specialist
Keith Glewen
Extension Educator