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CONSIDERATION FOR SOUND NITROGEN (N) INPUTS FOR THE 2017 CORN CROP

09/08/2016

Corn growers will best meet production goals for 2017 when all yield limiting factors are uncovered and are in sufficient supply to meet critical levels for crop growth and yield potential. (See Liebig's Law of the minimum demonstrated here.)

  • Nitrogen is the most commonly applied nutrient and one of the costliest inputs in corn production.  Mismanagement can limit yields, reduce profitability and contribute to negative environmental impacts.
  • Nitrogen residing in soils as applied fertilizers and N mineralized from organic matter is subject to the dynamics of soil moisture and temperature and must be managed as a system of interacting factors.
  • Land grant university recommendations are research-based and provide a firm foundation for nitrogen recommendations that are considerate of positive economics, while offering our industry a framework for nutrient applications that are defensible.

Below are the most important considerations for a profitable nitrogen management system

Maximum Return to Nitrogen (MRTN) rates as your base N rate. Traditional yield based rate recommendations have proven not to be very effective in predicting the right N rate for corn in the humid Midwest.  MRTN offers a more robust method that considers the economics related to the cost of N and crop selling price, making good rationale for environmentally defensible and an economically optimal approach to N rate.  Use this link to access the MRTN rate calculator. MRTN calculations are predicated on hundreds of data points over several site years and are modified as new yield data is entered. (See example below).

Splitting up nitrogen application timing and nitrogen source can more fully optimize your N program by hedging potential risks of N loss associated with weather extremes and more fully match adequate supply of nitrogen to crop uptake demands during the growing season.  When applying fall anhydrous ammonia target 60-70 percent of the total N needs (MRTN rate), followed by the remaining N needs as spring pre-plant incorporated,  early post-surface applied urea or urea ammonium nitrate (UAN) with a urease inhibitor. Local data from "On Farm" trials suggest a very good return on investment over a one time, one source N application.

Use of a Nitrification Inhibitor such as N-Serve® with fall anhydrous ammonia makes good economic sense and is environmentally responsible.   No applications of ammonia should occur prior to soil temperatures dropping to 50˚F and trending lower at a four inch depth, slowing the microbial conversion of ammonium (stable in soils) to nitrate (subject to leaching and denitrification loss).  The addition of N-Serve® to fall applied anhydrous ammonia further mitigates weather related nitrate loss while protecting yield potential by seven to eleven percent.

Monitor your system continually.  N-WATCH is a management tool that provides insight into the dynamics of plant-available nitrogen (nitrate and ammonium-N) in the upper two feet of the soil profile as the year progresses.   N-WATCH should stimulate new questions about the 4Rs of nitrogen, while helping us to understand N supply and demand dynamics.

Visit with your certified crop advisor for details about how to incorporate each of the considerations into your corn total fertility program.

Nitrogen Rate Charts.png


MRTN rate for corn following soybeans in central Illinois, with an N investment of $0.32/lb. and a corn price of $3.40 per bushel. The MRTN rate is 177 lbs. of N per acre and a range of 161-193 lbs/ acre gives a net return within $1.00/acre of the MRTN. Source: Iowa State University. N-Serve® is a trademark of Dow AgroSciences. 

Dan Maggart serves the FS System as GROWMARK manager, agronomy services. He can be reached at [email protected].

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