Posted by: usset001 | April 4, 2014

Delayed Planting and Corn Yields in Minnesota

cornrawIt is early April and already there is a lot of chatter about getting the crop in the ground in a timely manner. The winter was very cold, and the frost runs very deep. And over the past 24 hours, just about the time we thought we had the snow cover gone, Minnesota received the gift of 6 plus inches of heavy, wet snow. The concern is for another year of late planting, and a detrimental effect on corn yields. We have lots of numbers on Minnesota corn planting progress and yields – let’s look at them and see if we can make any sense of the data.

Studies show that late planting puts a drag on corn yields. I found a recent article from Jeff Coulter, Minnesota Extension Corn Specialist here. In a nutshell, Minnesota corn yields are optimized with planting dates of April 25 to May 10 (these are southern Minnesota conclusions). A rapid decline in corn yields would kick in when planting was delayed beyond mid-May. This is what the studies say – how well to the conclusions hold up over time?

I reviewed USDA Crop Progress reports from 1979-2013, focusing on corn planting progress in Minnesota. Crop progress reports are issued weekly and planting progress is estimated and reported every week the information is relevant. In most years, Minnesota has planting progress to report starting in the last ten days of April and ending in the first ten days of June. There are extremes. In 2012, USDA reported 1% of the Minnesota corn crop planted for the week ending April 8. In 1983, USDA reported the last 2% of the Minnesota corn crop planted during the week ending June 19.

Late planted years: I studied the planting progress reports and picked out four years – 1979, 1986, 1991 and 1996 – that stood out as late planting years in Minnesota. Each of these years had less than 80% (a range of 71-79%, to be exact) of corn planted as of the week ending May 24-30. For perspective, most other years showed 90-100% of the corn crop planted by this time. Figures in the table are bushels/acre.

MN trend yield    Actual yield     Actual vs. trend    Actual vs. trend (%)
1979         93.5                     100.0                           6.5                       7.0%
1986        108.2                   122.0                           13.8                      12.7%
1991         118.8                   120.0                           1.2                          1.0%
1996        129.4                   125.0                           (4.4)                      -3.4%
average 112.5                 116.8                         4.3                       3.8%

Despite late planting in these four years, Minnesota corn yields averaged nearly 4% above trend yields (my estimates of trend yields are based on a simple 30 year regression).

Early planted years: More years stood out as early planting years. What do the years these 11 years – 1987, 1988, 1998, 1999, 2000, 2003, 2004, 2005, 2007, 2010 and 2012 – have in common? In each of these years, the Minnesota corn crop was at least 85% planted as of the week ending May 10-16. Other years showed an average of 55% of the corn crop planted by this time.

MN trend yield    Actual yield    Actual vs. trend    Actual vs. trend (%)
1987                    109.3                    127.0                   17.7                          16.2%
1988                    111.9                       74.0                  (37.9)                     -33.9%
1998                   137.3                      153.0                  15.7                         11.4%
1999                   139.9                      150.0                  10.1                          7.3%
2000                   142.4                      145.0                 2.6                            1.8%
2003                    150.0                     146.0                (4.0)                        -2.7%
2004                    152.6                     159.0                   6.4                          4.2%
2005                    155.1                       174.0                 18.9                         12.2%
2007                   160.2                       146.0                 (14.2)                       -8.9%
2010                    167.8                       177.0                  9.2                           5.5%
2012                    172.9                        165.0                 (7.9)                       -4.6%
average           145.4                     146.9                 1.5                         1.0%

This is interesting! Minnesota corn yields averaged 1% above trend yields in the early planting years – worse than the late planted years. Clearly, 1988 is having a big impact on the average. Remove 1988 from the equation and you will still find that actual yields in the remaining 10 years averaged 4 % over trend, or the same as the late planted years.

What’s going on? Why does the data go against numerous studies that show early planting correlating with higher corn yields? One issue may be as simple as sample size. I have, after all, just four years to look at for late planted years.

The real issue can be found in the Latin phrase, “ceteris paribus” which means “all other things being equal.” Studies that examine planting dates and corn yields hold all other factors equal. The corn varieties used, the fertility of the soils, the number of growing degree days and moisture are all the same within the year (or years) of the study. Actual results from one year to the next are not ceteris paribus – growing degree days and moisture can vary widely from one year to the next. I’ll take this a step further and note that the most likely reason the early planting years were early was because the spring was warm and dry. Warm and dry springs make for early planting. However, if warm and dry persists, it can create crop development and maturity problems later in the growing season (and 1988 was the extreme example). A similar line of reasoning holds for the late years. Why were farmers late getting the crop planted in 1979, 1986, 1991 and 1996? I suspect it had something to do with a wet spring and, as the saying goes, rain makes grain.

In an ideal world, the corn crop would be planted early and ample summer rains combined with a long growing season would lead to a bumper crop. The world is rarely ideal. Today’s case in point is western Minnesota, where they need to replenish moisture in the soil if they want a good crop in 2014. I bet they’ll take this snow storm (and another) and a later planting date if it means replenished soil moisture.



  1. […] wisdom of seed companies that you have to get your corn planted by May 10.  Then I read an analysis by Ed Usset where he compared years of delayed planting with early planting.  Ed’s comparison found […]

  2. Hello Ed, for your readers. Grain Markets Logistics & Freight Report.

    • Your story was really initvmaofre, thanks!

    • Yuxiang,I have seen first-hand the practice of at least some Indian businessmen that will strive to please even to the point of losing money to ensure a good business relationship is maintained.This is at odds with the managerial economics that dictate that sometimes you should fire your customer. If they take an inordinate amount of time to service, unless there’s a really good reason, you should drop them and look for others.

  3. Excellent way of describing, and nice post to obtain data regarding my presentation focus, which i am going to present in college.

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