Planting Corn—Optimum Conditions and Anhydrous Applications

While frost-seeding may be a common practice for small grains and some legumes, planting corn into frosty soil conditions is never recommended.  Maximizing corn yield potential begins with identifying the optimum planting date and conditions. 

Planting Conditions. Corn requires a planting depth soil temperature of 50° F to germinate and grow.  Emergence can occur in as little as 13 days when the average soil temperature in the seed zone is 54° F.1 Temperatures that are below optimum can cause seeds to sit dormant, becoming more vulnerable to diseases and insects.  Ideally, corn should be planted when soil temperatures are optimal and within the target dates for the region.  For southern Minnesota, the optimum planting window is between April 21st and May 6th and a few days later in central Minnesota.1 In Wisconsin the optimal planting window is generally April 20th to May 5th for the southern portion of the state and April 30th to May 12th in the north.2

While the target planting dates for a region can be a good frame of reference, it is more important to plant when soil conditions are right for establishing a good seedbed.  Planting early can help maximize yield potential, but this advantage can be lost if planting occurs when soils are too wet.  To test if a field is fit to plant, take soil from the top 3 to 4 inches; soil should break apart when pressed between fingers, rather than forming a ribbon or ball.1  A firm seedbed is critical for establishing seed-to-soil contact and enabling good root growth.  Planting in soil that is too wet can lead to problems with sidewall compaction and restricted root growth.  

Anhydrous Ammonia. Anhydrous ammonia (NH3) can be a good, economical source of N for corn.  Under some circumstances, injury to corn seedlings from anhydrous ammonia can occur.  The risk of injury increases if soil is dry (limiting nitrification), the ammonia placement is too close to the seed zone, or the rate of application is too high.3  Injury has been observed on fine-textured soils, but is more common in coarse-textured soils.4  There is a greater potential for injury from spring applications due to the shorter window of time between anhydrous applications and planting.  To minimize the risk of injury, keep these tips in mind5:

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  • Anhydrous ammonia injections should be at a depth of at least 7 inches; shallower placement than intended can occur when application speeds are too great, causing knives to lift.
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  • Avoid planting corn rows directly over injection bands; applying NH3 at a slight angle relative to corn rows limits the number of plants placed directly over the band.
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  • Make sure that the soil closes behind the knife openings to reduce N loss and limit movement upwards towards the seed.
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Sources:
1 Coulter, J. 2010. Plan now for successful corn planting. University of Minnesota. http://blog.lib.umn.edu (verified 3/9/14); 2 Lauer, J. 1995. Corn hybrid response to planting date in Wisconsin. University of Wisconsin. http://corn.agronomy.wisc.edu (verified 3/9/14); 3 Sawyer, J. 2010. Corn injury from anhydrous ammonia. Iowa State University. http://www.agronext.iastate.edu (verified 3/8/14); 4 Overdahl, C.J. and G.W. Rehm. 1990. Using anhydrous ammonia in Minnesota. University of Minnesota. http://conservancy.umn.edu (verified 3/9/14); 5 Laboski, C. Planting corn immediately after anhydrous ammonia application, am I in for trouble? University of Wisconsin. http://www.soils.wisc.edu (verified 3/9/14).