ISU Agronomy Department Extension
  N-Rate Caluculator Help 07-07-2014

Corn Nitrogen Rate Calculator

More Info Material



University soil fertility specialists from the Corn Belt states began discussions in 2004 regarding nitrogen (N) rate for corn production. The reasons for the discussions centered on apparent differences in methods for determining suggested N rates across states, misperceptions regarding N rate guidelines, and concerns about application rates as corn yields have climbed to historic levels. An outcome of those discussions was an effort with the primary goal of developing an approach to N rate guidelines that could be utilized on a regional basis. A secondary goal was examining the most profitable fertilizer N rates for corn production across the Corn Belt.

This web site provides a method to calculate the return to N application and to find the maximum return to N (MRTN) at selected prices of N and corn directly from recent research data. The MRTN approach is the regional approach suggested for developing corn N rate guidelines in individual states. Nitrogen rate trial data is provided in this web site for seven states (Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin) where an adequate number of research trials (sites) were available for corn following soybean and corn following corn. These trials were conducted with spring, sidedress, or split preplant/sidedress applied N, and sites were not irrigated (except for those as indicated for irrigated sands in Wisconsin).



How to Use the Calculator


  • Choose if you want to calculate for one set of prices or multiple prices (price ratio of N and corn).
  • Choose which state you are interested in, or the region of a state or the soil yield potential grouping.
  • Choose the rotation, either corn following soybean or corn following corn.
  • Check if you want to include non N responsive sites (sites that had no yield increase to N application).
  • Choose the N fertilizer product and price, and corn grain price. If you use the multiple price ratio option, then you can choose four prices for N and corn grain (four ratios). The prices for N and corn have default values already entered. You may enter either the product cost ($/ton) or unit cost ($/lb N).
  • Hit the calculate button to run the calculations. This will take you to the results section. If you choose N or corn prices that are too high or low, you may get an error message in the results section. If that happens, please try another set of prices.



State Information


  • Illinois Geographic Region – Sites for Illinois are grouped by geographic location in the state: North, Central, and South. Northern Illinois runs from the Wisconsin border and includes those counties through which Interstate Route 80 runs. Southern Illinois includes the counties through which Interstate Route 70 runs, and the southern parts of counties (Shelby, Montgomery, Macoupin) north of those where soils have lower organic matter. Central Illinois is the area in between, and might also be considered to include southern portions of large counties (Henry, Bureau, LaSalle) through which I-80 runs. When in doubt in "border" areas, assign higher organic-matter soils to the northern of two areas and lower OM soils to the more southern area.
  • Indiana Geographic Region – Sites for Indiana are grouped by geographic region and general soil characteristic within the region. Indiana West and Northwest (INW), with silt loam and heavier textured soils. Soil series include Chalmers, Drummer, Raub, Toronto and similar soils in west central Indiana and Sebewa and similar soils in northwest Indiana. Indiana East and Central (INE), with silt loam and heavier textured soils. Soil series include Miami, Crosby, Celina, Cyclone, and similar soils in central Indiana and Blount, Pewamo, Morley, Haskin, and similar soils in northeast and east central Indiana. Indiana Remainder (INR), with silt loam and heavier textured soils. Areas of Indiana and soil series other than those listed in the above two areas.

  • Wisconsin Soil Yield Potential – Soil yield potential groups are designated for medium- and fine-textured soils and are based on soil properties such as drainage, depth of root zone, water holding capacity, and length of growing season. A list of soil series and the assigned yield potential category are provided in UWEX publication A2809 Nutrient application guidelines for field, vegetable, and fruit crops in Wisconsin. Coarse-textured soils (sands and loamy sands) are considered sands for the purposes of obtaining an N rate. Corn grown on sandy soils responds differently to applied N depending upon whether or not the field is irrigated. Thus, irrigated sands have been separated from non-irrigated sands.





  • EONR – Economic optimum N rate, the point where the last increment of N returns a yield increase large enough to pay for the additional N.
  • MRTN – Maximum return to N, the N rate where the economic net return to N application is maximized.
  • Maximum Yield –The yield where application of more N does not result in yield increase.
  • Net Return – The value of corn grain produced minus the N fertilization cost.
  • Price Ratio – The ratio of N fertilizer price to corn grain price ($/lb:$/bu).
  • Site – The land area occupied by a N rate trial, either replicated small plots in a specific field area or replicated field-length strips.
  • Site N Responsiveness – The corn grain yield increase with N application, non-responsive indicates no yield increase with N application while high response indicates large yield increase from N application.
  • Gross (Yield) Return – The value of corn grain increase due to N application.



Calculated Values

The results of calculations are provided in a table and in up to four graphs. Also, the chosen input information that went into the calculations is displayed.

Displayed Input Information

  • State.
  • The number of N rate trials (sites) that fit the chosen criteria and used in the calculations.
  • The rotation.
  • An indication if non-responsive sites are included in the calculations.
  • The N fertilizer and corn grain prices, and the price ratio(s).



  • MRTN Rate (lb N/acre), is the N rate at the MRTN. For the data set, rotation, and price ratio(s), the MRTN rate would be the suggested rate to apply for maximizing net return to N application.
  • Profitable N Rate Range (lb N/acre), is the N rate values at a $1/acre net return range (LOW and HIGH) around the MRTN. An N rate within this range around the MRTN would provide similar expected economic return and could be considered the profitable N rate range.
  • Net return to N at MRTN Rate ($/acre), is the economic net return at the MRTN rate.
  • Percent of maximum yield is the proportion of yield that might be produced at the MRTN rate and LOW/HIGH N rate range compared to the yield at the maximum response to N. It is not economical to attempt to apply N at a rate that would result in maximum yield or meet the N requirements of all sites (100% maximum yield), including the few most responsive sites. An economic rate will always result in less than 100% of maximum yield, that is, the MRTN rate will result in yield less than maximum. How far less than maximum depends on the price ratio of N and corn grain. For producers that are willing to tolerate more risk in their corn production system, then N application toward the LOW rate will have on average lower N input cost, but more frequently may supply N below maximum economic response. For producers with greater aversion to risk in their corn production system, then N application toward the HIGH rate will more frequently supply N that is at least adequate to meet corn N needs, but have on average greater N input cost and more frequently be above maximum economic response.
  • Nitrogen Product at MRTN Rate (lb product/acre), is the amount of product at the MRTN rate.
  • Nitrogen Product Cost at MRTN Rate ($/acre), is the cost of N at the MRTN rate.



Four graphs are available for viewing. Each presents a different component of the economic rate calculations, and compliment results shown in the table.

  • Return to N. This graph shows the two components for calculating net return across N rates; the gross return from yield increase and the fertilizer cost. The net economic return to N is the difference between these two values at each N rate. The point of maximum net return (MRTN, solid symbol) and the profitable N rate range (shaded symbol) within $1/acre of the maximum is shown on the graph. The N rate at the MRTN provides the greatest economic return to N application for the dataset, prices, and rotation chosen and would be the suggested N application rate. If multiple price ratios are chosen, then only net return to N is shown for each ratio.
  • Percent of maximum yield. This graph shows the percent of maximum yield across N rates for all sites in the dataset and rotation chosen. The N rate at the MRTN and the profitable N rate range (LOW - HIGH) within $1/acre of the MRTN are shown. As N rates move toward the LOW end of the range, the risk of having inadequate N increases and percent of maximum yield decreases, while as N rates move toward the HIGH end of the range the risk of having inadequate N decreases and percent of maximum yield increases. The greater the N cost relative to corn grain price (the larger the price ratio), the lower the economic rate, the farther the MRTN rate moves down the N response curve, and the more yield will be below the maximum yield. This graph helps with decisions regarding choice of N rate in regard to risk management. Reducing risk of insufficient N (that is, using a higher N rate) does result in greater N input cost, which in the long run could reduce economic return to N use. If multiple price ratios are chosen, then the percent of maximum yield is shown for each ratio.
  • EONR Frequency. This graph shows the frequency distribution, in 25 lb N increments, of the EONR for each site in the dataset and rotation chosen. The higher the bar for a N rate increment the more times sites had an EONR in that increment. Typically N trial datasets have a range of EONR values, with the most frequent range of EONR’s being around the MRTN value. If multiple price ratios are chosen, then the frequency of EONR is shown for each ratio.
  • EONR vs. Yield. This graph shows the relationship between the site EONR and yield at the EONR for each site in the dataset and rotation chosen. The number of symbols will match the number of sites in the dataset. You can scroll the cursor over the symbol to see the state, county, and manure history for that site. If multiple price ratios are chosen, then the graph will display the results for the first ratio.

Contacts for Additional Information and Questions

Regional Corn N Rate Publication

You can contact the extension specialist in your state if you have additional questions or are having difficulty with the calculations.

Illinois: Emerson Nafziger 217-333-4424
Iowa: John Sawyer 515-294-7078
Indiana: Jim Camberato 765-496-9338
Michigan: Kurt Steinke 517-355-0271 Ext. 1271
Minnesota: Dan Kaiser 612-624-3482
Ohio: Steve Culman 330-263-3787
Wisconsin: Carrie Laboski 608-263-2795