The April 28 crop report from the U.S. Department of Agriculture indicates only 4 percent of Minnesota corn acres are planted with the majority in southwestern Minnesota. In comparison, the 5-year average (2009 to 2013) is 30 percent. Many growers may not be able to resume field work until at least this weekend or early next week due to the recent and expected rainfall. This has led to questions about corn yield potential when planting is delayed.
University of Minnesota planting date studies show highest corn yield typically occurs when planting is completed by mid-May. In a study from 2009 to 2011 at Lamberton, Morris and Waseca that was funded by the Minnesota Corn Growers Association, average grain yield was within 98 percent of the maximum if planting was completed by May 15. Another study from 1988 to 2003 at Lamberton showed a May 15 planting date resulted in grain yields that averaged 95 percent of the maximum. These same studies found corn yield averaged 92 to 95 percent of the maximum when planting occurred by May 20.
Yield advantages associated with early planting typically are greatest when there is warm weather and rapid growing degree day accumulation between the first and second planting date windows. Corn emergence date is not likely to differ greatly between April 21 and May 5 planting dates this year given the limited growing degree days that have accumulated since April 21 and are expected over the next few days. This will likely result in similar grain yields between these planting dates, assuming that stand establishment with the early planting date is adequate.
Avoid field work in wet soil
Timely planting is important, although it is equally important to avoid tillage and planting when soils are too wet. In general, a field is fit for seedbed preparation when soil in the depth of tillage crumbles when pressed together rather than forming a ball.
Sidewall smearing can occur when double-disc openers cut through wet fine-textured soil, resulting in compacted soil around the seed that is difficult for nodal roots to penetrate. In addition, seed furrows can open up after fine-textured soil dries following wet conditions at planting, resulting in poor seed-to-soil contact and poor stand establishment.
Stick with planned hybrids
A general guideline for Minnesota growers is to stick with the planned seed choices until around May 21 to May 25 in order to maximize economic return. This is supported by a University of Minnesota study conducted at Lamberton and Waseca from 2010 to 2012 that was funded by the Minnesota Corn Growers Association. In this study, highest grain yield occurred with mid- and full-season hybrids (99- and 104-day relative maturity), even when the average planting date was as late as May 24. However, grain moisture at harvest was 2.3 percentage points higher with the 104-day hybrid than the 99-day hybrid with the late planting date (May 24).
When corn planting occurs between May 25 and May 31, it is wise to use hybrids that are 5 to 7 relative maturity units earlier than full season for the region. This reduces the risk of the corn being frozen in early autumn prior to reaching maturity.
Planting grain corn after May 31 carries high risk in Minnesota. If corn must be planted after
May 31 in Minnesota, growers can reduce their risk by planting hybrids that are about 15 or more relative maturity units earlier than full-season hybrids.
At June 5 or later, most growers in Minnesota that still need to plant should consider planting a crop other than grain corn if feasible. However, the decision of what to plant is also influenced by factors such as fertilizer applied and seed availability. These factors will need to be evaluated on a field by field basis.
Expected corn yields high
Most of the planted corn in Minnesota has been planted in fields with soil conditions that were suitable for preplant tillage and planting. However, cool and wet weather since the middle of last week is creating less than ideal conditions for germination and emergence. Seed quality in most planted fields should be fine, but it is a good idea to scout planted fields for seed quality once it dries out. This is especially true for low-lying poorly drained portions of fields that have received considerable rainfall since planting. Seed quality can be checked by digging up several planted seeds from different areas in a field and checking for seed firmness and discoloration. Seeds that are soft or discolored may have problems with emergence.
To see related tables and graphs of planting date and yield data, visit http://blog.lib.umn.edu/efans/cropnews/2014/04/weather-delays-corn-planting-b-1.html
Jeff Coulter is a corn agronomist with the University of Minnesota Extension.