It is generally acknowledged that the U.S. average corn yield is largely determined by weather conditions during the reproductive and grain filling stages during the summer months. Still, weather conditions during other times of the year, as well as the timeliness of planting, are known to influence the yield outcome. Prospects for completing planting of the 2018 corn crop in a timely fashion depend on four factors: 1) the percentage of the crop already planted; 2) the beginning date for a significant late planting penalty for corn yields; 3) the number of days suitable for fieldwork needed to plant the corn crop; and 4) the total number of days suitable for planting expected before the beginning date of a significant late planting yield penalty. The purpose of this article is to assess each of these factors and project the timeliness of planting the 2018 U.S. corn crop. We also consider the impact of the expected timeliness on projections of the U.S. average corn yield for 2018.
As outlined above, the first factor that will determine the prospects for timely planting of the U.S. corn crop is the percentage of the crop already planted. Given the cold and/or wet conditions experienced by nearly all of the Corn Belt this April, it is not surprising that the pace of planting has been slow. The USDA’s weekly Crop Progress report indicated that only 5 percent of the corn acreage in 18 major producing states was planted as of April 22, compared to 15 percent last year and a five-year average of 14 percent. Notably, 8 of the 18 states in the April 22 report had zero planting progress. By any measure, corn planting progress has fallen behind the normal pace.
The second factor that will determine the prospects for timely planting of the U.S. corn crop is the beginning date for a significant late planting penalty for corn yields. There is not complete agreement on the optimum planting window for maximizing corn yields or the date when late planting begins to impose a substantial yield penalty. Both the optimum window and cutoff date for a significant late planting penalty also varies by geographic location. For market analysis purposes, however, it is useful to identify one date for the end of the optimum window that can be applied to the entire Corn Belt. Acreage planted after that date would be considered to be planted late and yield potential would be expected to be reduced as the percentage of the acreage planted late increases.
In order to set the late planting cutoff date, we review information generated from agronomic research relating planting date to corn yields at the farm-level. We begin with information presented by Professor Emerson Nafziger in this March 23, 2017 article. It is typical of the information generated from agronomic research relating planting date to corn yields. The yield response curve in that article is based on an average of central and northern Illinois sites over 2007 through 2016. Professor Nafziger kindly provided the data in the form of yield penalty by planting date in Table 1. The yield loss in Illinois is minimized (optimal planting window) by planting in mid- to late April. The yield penalties become increasingly large as planting is delayed after mid-May. For example, planting on or after May 20 resulted in a yield loss of 4.2 percent, or 18 bushels per acre. See the farmdoc daily article of May 20, 2015 for further discussion of the response of yields to planting date in Illinois.
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