Corn planting date: Implications of planting in May

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In the prior posting on Farmgateblog you learned from two eminent corn production specialists that not having your corn planted does not make you naughty and destined for a time out in the corner of your machine shed. 

In fact, corn that has been planted in a few Corn Belt fields is struggling to survive in the cold, wet soil.  And once you get planting, some farmers may not stop, come darkness or even breakfast the next morning.  Which makes one wonder about the impact of planting late.

Since “Plant#13” is not getting underway until about the first of May in most parts of the Corn Belt, that means several weeks of April, in which corn is typically planted, will be shifted to May.  While that justifies the bigger planter to your lender and your spouse, it also indicates more corn will be planted later than usual. 

That is the premise of University of Illinois economists Darrel Good and Scott Irwin.

Is “later than usual” an indicator of future problems this year? 

While Purdue's Bob Nielsen and Emerson Nafziger of the University of Illinois tend to say no in the April 25 posting, Good and Irwin agree to some extend and say good yields can still be obtained based on prior years. 

However, everyone agrees that yields do decline at an accelerating rate in the later part of May.  And Good and Irwin rhetorically ask, “What is late, anyway?”

Their answer is: “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.” 

Looking at USDA data, they calculate that in the 42 years since 1971, about 15 percent of the corn crop was planted late, but varied widely depending on the season.

With only 4 percent of corn acreage planted by April 21, Good and Irwin say 81 percent of the crop needs to be planted before May 20 “when late planting begins.” 

Your ability to attend that party depends on the weather, and weather windows have been getting narrower, as indicated by the Good and Irwin research.  But after all that is why you have a bigger planter.  Good and Irwin say their research shows that for Illinois (you will have to calculate your own state) about 50 percent of the days in the last 10 days of April and the first 20 days of May are suitable for field work. 

At this point we are getting down to about a dozen days suitable for fieldwork before the arbitrary “late” flag is thrown.

Can your equipment cover the required territory? Do you have extra hours of labor you can call on? Do you have the capacity to go all night long? 

Some larger operations may already have a 24-hour schedule to cover tens of thousands of acres across many counties. 

Good and Irwin say you are planting 15-20 percent more acres in a day than in the 1970’s.  With their calculation that a suitable planting day will allow nearly 5 percent of the acreage to be planted, they figure by May 20 about 75 percent of the corn acreage will be planted.

With a quarter of the crop unplanted by May 20, that would equate to 2009, when yields hit a record high of nearly 165 bushels per acre. 

At a higher rate of planting per day, Good and Irwin calculate that only 9 percent of the crop would be unplanted by May 20 and considered “late.”

So what are the implications of a late planted crop?

  1. They say to reach the average of 15 percent of the crop unplanted by May 20, a higher rate of acres planted per day than the 10 year average will have to be achieved.  While some weather is expected to be good, there is also rain in the forecast and that may keep the planting rate behind average.
  2. The corn market has been softening for some weeks in reaction to recent USDA reports of large acreage, and new crop futures are as low as they were last June, prior to the onset of the drought.  Good and Irwin suggest the market is not concerned because of the prospect for large acreage and plenty of corn with a trend yield. The economists say that near perfect corn production weather followed the late planting season in 2009.


Recent planting trends indicate that an average of 15 percent of the corn crop is planted after May 20.  Based on the amount of corn planted to date, over 80 percent must be planted in the last 10 days of April and the first 20 days of May to take best advantage of higher yield opportunities.  Also based on the typical amount of suitable field work days, that amount is cut to about 15, making the planting window smaller. 

While increased acreage can be covered in a day with larger equipment, between 5 percent and 6 percent of the expected corn acreage must be planted per day between now and May 20, when yields taper off at a higher rate.

Source: FarmGate blog

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