The spring rains that have improved soil moisture conditions in many areas have been welcomed as favoring a return to more normal corn yields in 2013 following the drought of a year ago.
At the same time, persistent and heavy precipitation (including snow in northern areas) that has delayed the start to corn planting raise concerns that late planting will have a negative impact on yield potential.
Planting date, of course, is not the only factor and probably not the most important factor impacting corn yields. There are ample historical examples of late planted crops that yielded near or above trend value, early planted crops that yielded below trend value, and timely planted crops that yielded both above and below trend value.
Still, timeliness of planting is an important consideration for yield potential at this stage of the season. Here, we address the likelihood that a larger than average percentage of the corn crop will be planted late this year.
click image to zoom The first challenge in this analysis is to define late planting. The impact of planting date on potential corn yield has been clearly identified by agronomic research. That research generally shows, with all other conditions equal, that optimum yield potential is maintained over a fairly wide window of planting dates, but declines at an increasing rate for planting dates after the optimum window. For example, Figure 1 shows the results from agronomic experiments investigating the effect of planting date on corn yield in central Illinois. This research finds that, all else equal, average corn yields are not found to be substantially different for planting dates ranging from early April to mid-May. Yields generally decline at an accelerating rate for planting dates after mid-May. However, since planting dates have generally become earlier over time, yield response to planting date is non-linear, and planting occurs at different times in different regions, defining late planting over time for the U.S. is not straight-forward. In previous analysis we have quantified late planting as the percentage of the U.S. crop planted after May 30 in years prior to 1986 and after May 20 since 1986. That quantification balances the results of agronomic research and regional considerations and is used here.
Based on planting progress data as reported in the USDA's weekly Crop Progress report for the major corn producing states and the previous definitions of late planting, we calculate that an average of 15 percent of the U.S. crop was planted late in the 42 years from 1971 through 2012. The percentage of the crop planted late ranged from one percent in 1977 to 47 percent in 1995. Other years with more than 25 percent of the crop planted late included 1993, 1996, 2002, and 2009. Other years with less than five percent of the crop planted late included 1971, 1980, 1985, 2000, and 2012.