May 9, 2011
The temptation to get in the field and plant corn as soon as soils even look like they're ready may seem like an itch you just can't scratch hard enough. Resisting the temptation to go so quick that you create problems later will be tough.
Here's some information to help you decide how long you want to wait once soils begin to dry out before you try to get some corn in the ground. This data is taken from the Purdue University Corn & Soybean Field Guide, the pocket edition that fits in every glove box.
Agronomists talk about a yield penalty for every day of delay in corn planting after May 10 to May 15. Remember that those are averages, and no guarantee of what might happen in any one year.
According to the chart in the 2012 edition, page 13, if you plant May 15, you can achieve 95% of the potential yield compared to planting the crop April 30, assuming you have 30,000 plants per acre. The yield potential of April 30 planting at full population drops below 90% at populations between 22,000 and 24,000 plants per acre. Obviously, it's important to take steps necessary to achieve a good stand once you are able to plant corn.
If you plant May 20 and achieve 30,000 plants per acre, you still have 91% of original potential yield. If that was 200 bushels per acre, you could still be looking at 182 bushels per acre, on average. By May 25, it slips to 87%.
The penalty becomes somewhat steeper as you move toward and into June. If you plant on May 30, on average, compared to planting April 30, and have 30,000 plants per acre, you can expect 81% of optimum. Now you're talking 162 bushels per acre as the average yield. Remember, however, in test plots in 2010, yields above 200 bushels per acre for certain hybrids were achieved, even though the plot was planted the week of May 25. Populations were at or slightly above 30,000 plants per acre.
By June 4, you're looking at 75%, and by June 9, about 68%, or roughly two-thirds of what you would hoped to achieve. This data was put together by Emerson Nafziger at the University of Illinois.
The flip side is how much you lose if you leave slots open because it's too wet, create sidewall compaction that could affect emergence, or create soil compaction by disking or running over soil that's too wet. There are no tables on that one.
Gary Steinhardt, Purdue Extension agronomist, studied the effects of soil compaction nearly three decades ago. It is such an inconsistent variable that it is nearly impossible to put a figure on the amount of loss you can expect. However, he made three key observations.
One- the effect will be worse if it turns dry late in the season. That's true even if the crop emerges normally and you have a good stand. The roots could be impacted later if it's dry. If it keeps raining, effect may be minimal in the year the soil compaction is created.
Two- the effect will likely last more than one year. Even Steinhardt admits that sometimes creating some soil compaction is a cost of doing business if you're in dire straits. But recognize that the effects of compaction could show up two or more years down the road.
Three- The effect of soil compaction this year and in subsequent years, even if it's dry, will be worse for corn than soybeans. For whatever reason, soybeans seem better equipped to handle compacted soils and still produce reasonable yields.
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