According to the USDA/NASS, for the week ending May 5, only 2% of Ohio’s projected corn acreage was planted — compared to 20% last year and 27% for the five-year average. Persistent rains and saturated soil conditions have delayed corn planting. The weather forecast this week indicates the likelihood of more rain, so it is probable that many soggy fields may not dry out soon.
Long-term research by universities and seed companies across the Corn Belt gives us a pretty good idea of planting date effects on relative yield potential. The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. In the central Corn Belt, estimated yield loss per day with delayed planting varies from about 0.3% per day early in May to about 1% per day by the end of May, according to Bob Nielsen at Purdue University. These yield losses can be attributed to a number of factors including a shorter growing season, greater disease and insect pressure and higher risk of hot, dry conditions during pollination.
Given these planting date effects, do yield losses associated with late plantings translate into lower statewide yields? Not necessarily. Let’s consider some previous growing seasons that were characterized by a “late start” and what impact this had on crop production. For the purposes of this discussion, we will consider “late start” years as those in which 40% or more of the corn acreage was not planted by May 20. Since 1980, there have been significant planting delays associated with wet spring weather in 11 years — 1981, 1983, 1989, 1995, 1996, 2002, 2008, 2009, 2011, 2014 and 2016.
Of these eleven years, the greatest delays in crop planting occurred in 2011 when only 19% of the corn acreage was planted by May 30. In five of the eleven years (1981, 1983, 1996, 2002, and 2008) average state yields were markedly lower than the state average yield of the previous five years. In six of the eleven years, average yields were five bushels per acre or more below the yield trend line for Ohio. In one of these years, 2002, the average corn yield dropped to 89 bushels per acre (nearly comparable to the record low of 86 bushels per acre for the major drought year of 1988). However, in six of the eleven years, yields were similar or higher than the statewide average yield of the previous five years, and in one of these years, 2014, a record high corn yield, 176 per acre, was achieved.
In 2017, 73% of the corn crop was planted by May 20 (which does not categorize 2017 as having a “late start”). However, field agronomists and county ag extension educators estimated that as much as 40% or more of the corn planted in late April of 2017 was replanted in parts of Ohio due to excessive soil moisture, freezing temperatures and frosts, fungal seed decay and seedling rots, and soil crusting. (NASS does not report replanted corn.) Nevertheless, the yield in 2017 was a record 177 bushels per acre, 16 bushels above the yield trend.
This comparison of statewide average corn yields from past years indicates that lower grain yields are not a certainty with late plantings. While delayed planting may cause yield loss relative to early planting, planting date is just one of many factors that influence corn yield. There are other factors that are of greater importance than planting date in determining grain yield. Weather conditions (rainfall and temperature) in July and August are probably the most important yield determining factors. Favorable weather conditions subsequent to planting may result in late planted crops producing above average yields, as was case in 2009 and 2014. However, if late planted crops experience severe moisture stress during pollination and grainfill, then crop yields may be significantly lower than average, with 2002 being the most notable example.