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U OF ILLINOIS ECONOMIST REPORTS ON YIELD IMPACT OF LATE CORN PLANTING
Blog by Scott Irwin, Department of Agricultural and Consumer Economics, University of Illinois

Cold and wet weather has delayed the normal pace of corn planting this spring. The latest weekly Crop Progress report from the USDA indicates that only seven percent of the 2022 U.S. corn crop was planted as of April 24th and just two percent in Illinois. The normal pace for this week is 15 percent for the U.S. and 21 percent for Illinois.



A key concern in the market is the impact that planting delays may have on the U.S. average yield of corn. There is heightened interest in this question at the present time given the tight global supply and demand situation for corn and near record high prices. We reviewed data from agronomic field trials in a recent farmdoc daily article (April 14, 2022) and this data indicates there are substantial yield penalties for late planting of corn beginning around mid-May.

In another recent farmdoc daily article (April 21, 2022), we showed that maximum planting rates per suitable field day in the heart of the Corn Belt have increased very little over time and that it still takes a minimum of about 14 days, or two weeks, to plant the corn crop. The purpose of this article is examine what we know about the relationship between late planting and the U.S. average yield of corn.

Analysis
The starting point for the analysis is defining 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 cutoff date for late corn planting in the U.S., we follow our previous work on the topic (e.g., farmdoc daily, May 20, 2015; April 24, 2019; May 13, 2020). The cutoff date is based on agronomic field trials relating planting date to corn yields at the farm-level (e.g., farmdoc daily article, April 14, 2022), which indicates that yield penalties become increasingly large as planting is delayed after mid-May.

As before, we define the beginning date for substantial late planting penalties on corn yield in the U.S. to be May 30th from 1980 through 1985 and May 20th from 1986 onwards. The change in cutoff dates in the mid-1980s reflects recommendations for earlier planting that appeared around that time.

Figure 1 shows the percentage of corn planted late in the U.S. based on these definitions over 1980 through 2021. On average, late planting was 17.6 percent, with the bulk of the observations between about 5 and 25 percent. The extraordinarily high level of late planting in 2019 is obvious. At 50 percent, this was the highest level of late planting over the 42-year sample period.

There were only two other years (1993 and 1995) when late planting exceeded 40 percent. Finally, there is no evidence of a trend up or down over time in the late planting percentage, which suggests that producer behavior in aggregate with respect to late corn planting has been quite stable (after adjusting for earlier planting through time).

The next step of the analysis is to estimate the impact of late planting on the U.S. average corn yield. Figure 2 show the relationship between the trend deviation for U.S. corn yield and corn acreage planted late over 1980 through 2021. The trend deviation is computed based on a linear trend for U.S. average corn yields over this period.

The figure shows that, as expected, there is an overall negative relationship between late planting and corn yield deviations from trend. Specifically, for a 10 percent increase in late planting the U.S. average corn yield decreases by about 2 bushels per acre. It is also interesting to consider the implication of the intercept estimate of the regression model. It implies that when late planting is zero the increase in corn yield above trend is 3.4 bushels.

This is the maximum benefit of early planting on the U.S. average yield of corn according to this regression model. In comparison, the maximum loss in yield from high levels of late planting can be much larger. For example, the model predicts that the 50 percent level of late planting in 2019 leads to a 6.3 bushel decline below trend for the U.S. average corn yield.

To view the complete report, click here.


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