Spring rains in many areas have been welcome following last year's drought, however, persistent and heavy rain and snow that has delayed planting is raising worries about a negative impact on yields this fall. While planting date is not the only factor that impacts corn yields, timeliness should still be an important consideration at this stage of the growing season.
In this report, we examine the likelihood that a higher than normal portion of the corn crop will be planted late this year.
The first challenge is to define late planting. Research on the impact of planting date on potential corn yield 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. 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 (PDF) 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.