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OSU Extension

College of Food, Agricultural, and Environmental Sciences

April 30, 2019 - 8:28am --

Planting season has arrived and while there are some acres planted in the Wayne County area, many fields are wet.  Today, I want to address two common questions regarding corn planting, soil condition and determining a nitrogen rate application.

Planting date is one of the most important factors that affects corn yield potential.  The Ohio Agronomy Guide bulletin says that the recommended planting dates for corn in northern Ohio is April 15 to May10.  According to a planting date table in the Ohio Agronomy Guide, planting from April 23-29 is most likely to allow for 100% of maximum yield with yield potential declining for later planted corn.  However, Extension corn specialists and agronomists across the corn belt caution that growers need to pay attention to soil conditions in addition to planting date.  Peter Thomison, OSU Extension corn specialist, and Steve Culman, OSU Extension soil fertility specialist, advise in a recent CORN newsletter article to avoid tillage and planting operations when the soil is wet. Quoting from that article, “Yield reductions resulting from "mudding the seed in" are usually much greater than those resulting from a slight planting delay. Yields may be reduced somewhat this year due to delayed planting, but effects of soil compaction can reduce yield for several years to come. Keep in mind that we typically do not see significant yield reductions due to late planting until mid-May or even later in some years. In 2017, favorable growing conditions allowed many growers to achieve exceptionally grain high yields in corn planted as late as early June.”

Soils are easily compacted when they are wet and planting into wet soils can result in sidewall compaction that does not allow corn roots to penetrate down into the soil.  According to an April 19, 2019 article by Paul Jasa, Extension Engineer from the University of Nebraska, one of the primary factors involved in sidewall compaction is planting corn too shallow.  The target goal for corn planting depth is two to three inches deep.  The closing wheels on corn planters are designed for this depth, so that the sidewalls of the seed furrow are fractured as the soil closes around the seed.  Sidewall compaction will also result when press wheels are set with too much downward pressure.  Excessive downward pressure, combined with shallow planting depth results in press wheel compaction below the seeding depth, which will make it difficult for seedling roots to penetrate down into the soil.  According to Jasa, “down pressure on the press wheels should be checked at seeding depth, not at the top of the seed-vee. If the seed-to-soil contact is adequate, don't tighten the down pressure springs trying to close the top of the seed-vee.”

Recently I had someone ask me about the thumb rule for nitrogen application to corn. They wanted to know how many pounds of nitrogen to apply per bushel of corn yield.  While nitrogen is critical in determining corn yield, land-grant Universities throughout most of the corn-belt no longer provide nitrogen recommendations based on a per bushel yield goal.  There are several reasons for this.  In the past, nitrogen prices contributed to a philosophy of cheap insurance, apply more than enough.  Today’s nitrogen prices no longer make it a cheap insurance.  Additionally, applying more than enough nitrogen is not environmentally friendly or responsible.  Another very important reason is that the pounds of nitrogen per bushel recommendation implied a straight-line relationship between yield and nitrogen rate.  Analysis of multiple years of corn nitrogen trials across the corn belt show that the relationship is curvilinear.  The first units of nitrogen provide the greatest yield response and at some point, additional nitrogen no longer provides a yield benefit.  Even before that point, the additional yield does not cover the added expense of additional nitrogen.  Finally, analysis of corn nitrogen trials across years and locations indicates that soil mineralization rates and weather conditions are major determinants of corn yield.

The current recommendation is the use of an economic calculator to determine nitrogen rates.  Corn yield responses along with corn and nitrogen prices are used to calculate the point at which the last unit of added nitrogen returns a yield increase large enough to pay for the added nitrogen cost. This approach is termed the maximum return to nitrogen (MRTN).  The MRTN approach requires three inputs: the previous crop grown (corn or soybean), price of nitrogen fertilizer, and price received per bushel of corn. When corn prices are low, nitrogen rates are reduced; when corn prices rise, recommended nitrogen rates increase. Similarly, the model responds to nitrogen prices, recommending high nitrogen rates when nitrogen costs are low, and reduced rates when costs are high. The model is housed on an Iowa State University website, but each state provides their own yield response data and some support for website maintenance and updates. When a user selects Ohio as a state, they will only find data collected from trials in Ohio.  Access the tool online at

Contact the Wayne County Extension office at 330-264-8722 for more information about the nitrogen rate calculator.


Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.

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