Thread by @ScottIrwinUI

1. My next thread deals with the yield impact of late corn planting. We looked at three approaches to estimating impact on US avg corn yield in a #FDD article last week farmdocdaily.illinois.edu/2020/05/the-im…

2. The first method simply regressed trend deviation for US avg corn yield on the measure of late planting. Slope is -0.2, or decline of 2bpa for each 10% increase in late planting. Notice how well that fit the obs for 2019.

3. The explanatory power for this regression is low because we took trend out and only included one variable---late planting. Did not account for any weather impacts. Could result in a biased regression coefficient estimate due to "omitted variable bias."

4. So, we also estimate a crop weather regression model for US avg corn yield. Included trend, late planting, and monthly precip and temp variables. The full enchilada. coefficient estimate was -0.22, almost same as simple one variable model.

5. Final approach was different. Rather than using time-series data we used a cross-section of states for 2019. Idea is that variation in late planting and yields across major Corn Belt states is another way to identify the relationship.

6. Despite the extreme simplicity of this cross sectional approach, we get a very comparable estimate of -0.17. For each 10% increase in late planting across these 10 states in 2019, state corn yield dropped 1.7bpa.

7. In sum, all three methods yield an estimate very close to -0.2, implying that a good rule of thumb is a loss of 2bpa for every 10% that planting on May 20th is above the long run average of 17.7%. Good to know.

8. A real asymmetry in late planting impacts on yield that can be missed. Gain for early planting (0 late planting) is about +3.5bpa above trend but loss from late planting can be much larger, such as almost 7bpa in 2019.

9. Finally, the kind of late planting impacts discussed in this thread and in the article are related but different than those in agronomic planting date trials. Apples and oranges. Not directly comparable.

10. Here is the link to the #FDD with all the details farmdocdaily.illinois.edu/2020/05/the-im… Up next later this week---late planting and soybean yield.