This blog item is being written during a record-hot Tuesday afternoon, May 14, in Omaha. But, the subject is still a prime one for consideration, and that is whether the late start that corn planting has had this season will indeed result in sub-par yields.
USDA, of course, already weighed in on that issue in the May 10 supply-demand report with the projection of 158 bushels per acre for U.S. corn yields. That was a reduction of 5.6 bu/A from the projection of 163.6 announced at the Ag Outlook forum back in February. DTN contributing analyst Joel Karlin noted in an e-mail exchange that this is in line with crop weather research which was presented at the Outlook Forum. In that presentation, the USDA researchers have a mid-May planting progress coefficient of 0.289. So, a 10 percent slower pace would reduce corn yields by 2.89 bushels per acre assuming everything else stayed the same. "With the USA dropping its yield by 5.6 bu/A from their Feb Ag Outlook they are figuring mid-May plantings will be 19 percent behind average and I can’t really quarrel with that," Karlin said.
There is, of course, plenty more material on this subject. A recent edition of the Indiana crop weather report featured an article on late planting and yield impact by agronomist Bob Nielsen. Pertinent excerpts from that article are presented here.
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What are the consequences of a delayed start to planting? How important a predictor of statewide corn yield is planting date anyway? Does late planting in and of itself guarantee lower than normal yields?
Good questions, but the effect of planting date on statewide average corn yield is not clear-cut.
If one reviews USDA-NASS crop progress reports for the past 20 years, there is NOT a strong relationship between planting date and absolute yield on a statewide basis for Indiana. Specifically, departures from annual trend yields are not strongly related to corn planting progress.
Even though one can statistically define a mathematical relationship between departure from trend yield and planting progress by April 30 or May 15, the relationship only accounts for 22 to 24 percent of the variability in yield trend departures from year to year.
In other words, a number of yield influencing factors (YIFs) in addition to planting date also affect the ultimate absolute yield for a given year.
Here's the Conundrum
Why is it that every corn agronomist known to man preaches about the importance of timely planting and yet the statewide statistical data suggest that planting date accounts for only 23% of the variability in statewide yields from year to year? Let's look more closely about this seeming conundrum.
It is true that corn grain yield potential declines with delayed planting after about May 1 (Myers & Wiebold, 2013, Nafziger, 2008; Nafziger, 2011). Estimated yield loss per day with delayed planting varies from about 0.3 percent per day early in May to about 1 percent per day by the end of May.
Yield potential goes down with delayed planting because of a number of factors, including a shorter growing season, greater insect & disease pressure, and higher risk of hot, dry conditions during pollination.
However, the good news is that planting date is only one of many YIFs for corn. What is important to understand is that yield loss due to delayed planting is relative to the maximum possible yield in a given year.
In other words, if all the other YIFs work together to determine that the maximum possible yield this year for the optimum planting date is 220 bushels per acre, then the consequence of a 10-day planting delay beyond April 30 (at 0.3 percent decrease per day) would be a yield potential of about 213 bu/A (i.e., 220 bushel potential minus [10 days x 0.3 percent] due to delayed planting).
However, if all the other YIFs work together to determine that the maximum possible yield this year for the optimum planting date is only 150 bu/A, then the consequence of a 10-day planting delay beyond May 1 (at 0.3 percent decrease per day) would be a yield potential of about 146 bu/A (i.e., 150 bu/A potential minus [10 days x 0.3 percent] due to delayed planting). Make sense?
Consequently, it is possible for early-planted corn in one year to yield more than, less than, or equal to later-planted corn in another year depending on the exact combination of YIFs for each year. Farmers know this to be true because some have had June-planted crops in recent years that ultimately yielded better than any crop they have ever had---because the remainder of the growing season following the delayed planting was exceptional.
For example, the crop years 2012 and 2009 represent early and late planting date years in Indiana. About 94 percent of the state's crop was planted by May 15 in 2012, but only 20 percent of the crop was planted by May 15 of 2009. Yet, the earlier planted 2012 crop yielded 38.7 percent BELOW trend yield for that year and the later planted 2009 crop yielded 9.3 percent ABOVE trend yield. Why? Important differences in YIFs between the years other than simply the planting dates.
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