The initiation of full-scale corn planting  has been delayed across most of the Upper Midwest due to continued wet weather and cold soil conditions. A few farm operators were able to plant a limited amount of corn  during the period of April 25-29 in some portions of southern Minnesota and northern Iowa. However, no corn is planted in most portions of the region. By comparison, nearly all of the corn, and a substantial amount of soybeans, was planted by early May in 2010, and field conditions were excellent. Nationwide, experts are saying that this is among the latest corn planting dates we have seen in the past decade, and in some areas it is the latest since the disastrous year of 1993.
Estimates are that only 13% of the corn nationwide was planted by May 2, which is far below last year’s record planting pace of 66%, and compares to a 5-year average of 40% planted by that date. In Minnesota, only 1% of corn was reported planted by May 2, compared to a five-year average of 46% by that date, while in Iowa only 8% of the corn was planted, compared to a five-year average of 48%.
Most of Southern Minnesota and Northern Iowa received 1-2 in. of rain from April 24-30, which fell on top of soils that were already close to saturation in most areas. Rivers, streams and drainage ditches are near capacity at a many locations, which means the field drydown process is slowed compared to normal. At the University of Minnesota Research and Outreach Center  at Waseca, the total precipitation for the month of April (as of April 29) was 4.30 in., compared to a normal of 3.23 in. Precipitation was recorded at Waseca on 21 days during April.
The other big issue this spring has been soil temperature. The daily average 2-4-in. soil temperature was well below 50° F on May 1 in most areas of Minnesota and northern Iowa. A soil temperature of 50° is usually recognized as the minimal planting zone soil temperature for acceptable corn planting conditions. At Waseca, the average 2-in. soil temperature on April 29 was 43.5° F, while the average soil temperature at the 4-in. depth was only 42.5°. The average 2-4-in. soil temperature at Waseca barely reached 50° on only a few days during April. The average air temperature at Waseca during April was 43.6°, compared to a long-term average of 44.9°; however the last half of April was far below normal temperatures.
According to research studies, at 50° F it takes corn nearly three weeks to emerge, compared to an emergence time of about 10 days at 60°. Once we reach May 1, most crop experts would recommend planting the corn once field conditions are fit, regardless of soil temperatures, due to potential yield losses associated with later planting dates.
We will soon reach the point in southern Minnesota where optimum yield potential starts to decline with the full-season corn hybrids . Most university and seed company research shows that optimum yield starts to decline with corn planting dates after May 5-10; however, yield declines become much more significant with corn planting dates after May 20. Most experts recommend that growers stay with their full-season corn hybrids until at least May 25, because the shorter-season corn hybrids have much lower yield potential than the full-season hybrids.
The later corn planting dates also increase the likelihood of increased corn drying costs in the fall, due to the later maturity dates of the corn. We are now also entering the optimum time for soybean planting , so most farm operators will begin planting soybeans  as soon as they complete corn planting.
Editor’s note: Kent Thiesse is a former University of Minnesota Extension educator and now is Vice President of MinnStar Bank, Lake Crystal, MN. You can contact him at 507-726-2137 or via e-mail at [email protected]