Cold, wet conditions have delayed corn planting throughout Ohio. According to the USDA/NASS (http://www.nass.usda.gov/), for the week ending May 15, corn was 34 percent planted, which was 37 percent behind last year and 20 percent behind the five-year average.
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 (Nielsen, 2015). 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 I’ll 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 nine years – 1981, 1983, 1989, 1995, 1996, 2002, 2008, 2009, and 2011. Table 1 shows the percentage of corn acreage planted by May 20 and May 30, the 50% planting date (the date by which 50% of the corn acreage was planted), yield, the state average yield for the previous five years, and the departure from the yield trend in each of those years. Of these nine 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 nine 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 nine 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 88 bushels per acre (nearly comparable to the record low of 86 bushels per acre for the major drought year of 1988). However, in four of the nine years, yields were similar or higher than the statewide average yield of the previous five years, and in one of these years, 2009, a record high corn yield, 174 per acre, was achieved.
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. Figure 1 shows grain yields associated with dates by which 50% of the corn acreage was planted in Ohio from 1980 to 2012 and it does not suggest a strong relationship between planting date and 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. 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 in addition to 1981, 1983 and 1996.
Nielsen, R.L. 2015. The Planting Date Conundrum for Corn. Corny News Network, Purdue Univ. [online] https://www.agry.purdue.edu/ext/corn/news/timeless/PltDateCornYld.html [URL accessed May 16, 2016].