NDSU Extension - Ramsey County


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August 29, 2011 Agriculture Column


Questions have been asked about Growing Degree Days and how our corn is sitting at this point of the growing season.  Some might suggest that the growing degree units, for our area, is 1716 as of today but that is based on a May 1 planting date.  We all know that we did not get planting on May 1, it was more like May 22 when most everyone got planting.  Using May 22, as the start date, we find we are at 1548 GDD’s.  Using that number and knowing that 80 day corn needs 2050 growing degree units means we will need another ???????  I put the questions marks as we are not sure how many more days we will need.  If the air temperature would be 80 degrees during the day and 60 during the night time hours we would only need another 33 days to reach physiological maturity or black layer, but if daytime air temperatures are 60 degrees we will need an additional 67 days of frost free.  To calculate Growing Degree days you use the high temperature of the day, with a maximum temperature of 86 degrees, add to that number the low temperature of the day, with a minimum of 50 degrees.  Subtract 50 from that number and divide by 2.  This will give you the GDD’s for that day.  Example:  90 degree day temperature and 46 degree night temperature equals:  86+50 subtract 50 and divide that number by 2== 18 gdd’s for that day.  So what will the fall bring obviously not those kind of numbers but who knows????  



 Fall Nitrogen Application

Although fall‐applied fields often suffered more loss than spring‐applied fields, it is not always the case. Growers that applied late in the fall when our recommendations would suggest it was safer are more satisfied with their results than those that were early. For those who cannot recall our recommendations for fall nitrogen timing, here they are again.

1. Do not fall apply N on soils that typically flood in the spring or to soils with sandy loam or coarser textures.

2. Do not even think about applying anhydrous ammonia until October 1.

3. After October 1, check the soil temperature measured at 4 inch depth from 6‐8AM. When it hits 50 F, it is practical to apply anhydrous ammonia (but not urea!)

4. A week after the date for anhydrous ammonia, growers can start applying banded urea.

5. 2 weeks after the date for anhydrous ammonia, growers can start broadcast‐incorporating urea.


This past season, the date the soil temperature dropped to 50 F was about October 15. That means that banded urea application should not have begun until October 22 and broadcast urea until October 29. There is nothing wrong with well‐timed fall N application in North Dakota. In years of dry weather, it didn‟t matter when nitrogen was applied. If the last 18 years of wetness is an indication of the beginning of a trend, we think that this winter and spring will also be wet and we will be set up for losses for N that was applied too early. Agronomy does not always mesh with convenience. Although many growers have a „harvest gap‟ in September after small grain harvest and before soybeans/corn/sunflower, it is not the time to fall apply N. P and K can be applied during this time, but not N. Too many bad things can happen to

early applied N if it is applied too early with too much fall ahead of it. A nitrification inhibitor should be used not to move the date of application earlier, but to protect the N‐applied at a safer date from unanticipated losses from early spring wetness. N‐Serve™ can be applied with anhydrous ammonia to protect N from losses due to nitrification in the fall/spring. Instinct™ is an encapsulated form of nitrapyrin (active ingredient in N‐Serve), and the label we have currently lists it as a spring additive with urea or UAN. Check with your Dow‐ Agro Sciences rep to see if it is labeled for fall application with urea. In the spring, products with the additive DCD (examples are Super‐U™ by Agrotain, Int., or Guardian™ by Conklin) will also slow nitrification. One product that is sold as a nitrification inhibitor, but does not function like one is Nutrisphere™. It is neither a nitrification inhibitor nor a urease inhibitor and should not be used as one.


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