Corn nitrogen rate calculator may improve grower profitability

Delayed planting and wet weather forecast means there is still time to adjust at-planting or sidedress nitrogen applications.

A few simple steps may increase grower confidence in determining total nitrogen applications. The “Corn Nitrogen Rate Calculator” is a web-based tool to help determine nitrogen application rates and is hosted on the Iowa State University Extension website.

Due to inconsistencies between recommendations and the economic optimum nitrogen rate, soil fertility specialists from across the North Central region began developing and implementing a change from a yield-based approach to the Maximum Return to Nitrogen (MRTN) approach. Amongst several factors, this approach takes into account the value of corn grain and the cost of nitrogen fertilizer when determining the most economic optimum nitrogen rate.

Following is a series of screen snapshots of the calculator tool taken directly from the ISU Extension website. The numbers and corresponding descriptions provide a step-by-step how-to guide in using this technology.

Corn Nitrogen Rate Calculator. Corn Nitrogen Rate Calculator.

1. Start page. This is the initial screen you will view when entering the N rate calculator website. For a more in-depth description of the calculator, click on “Regional Corn N Rate Publication.”

2. Choose a state. Use the scroll menu to find and highlight “Michigan.” Although ISU Extension hosts the calculator, rates are based on state-specific nitrogen response trials conducted throughout the state. Response trials are established each year in Michigan, and the database is continually updated.

3. Choose a rotation pattern. Currently, calculations are only available for corn following soybean rotations. Future studies will incorporate data for corn following corn. For current corn following corn nitrogen recommendations, refer to Michigan State University Extension Publication E-2904 Nutrient Recommendations for Field Crops in Michigan.

4. Include non-responsive sites. Check this box if you would like to include non-responsive sites, which are sites that demonstrated no yield increase due to nitrogen application.

5. Choose form of nitrogen fertilizer and cost and corn price. From the scroll-down menu, choose the form of nitrogen fertilizer you are applying. Available options include anhydrous ammonia, UAN (28 or 32% N), urea and ammonium sulfate. Next to the chosen nitrogen source, enter the current cost of nitrogen fertilizer in dollars per ton and the expected corn price in dollars per bushel. The cost of the chosen nitrogen fertilizer will automatically be converted into dollars per pound of nitrogen.

6. Calculate. Click the “calculate” button to go to the next page where the nitrogen rate calculations will be displayed. “Reset” will clear the information already entered in order to start the process over.

7. Calculation page. This will be displayed after clicking the “calculate” button. At the top of the page, the information previously provided will be shown (state, nitrogen cost, corn price, rotation, and whether or not responsive sites are included). The number of sites in the database will also be displayed – 32 for Michigan – along with the price ratio of nitrogen fertilizer (dollars per pound of N) and corn price (dollars per bushel).

8. MRTN rate. The MRTN rate is the nitrogen application rate where economic return to nitrogen application is greatest. In this example, this rate is 130 lbs. N/acre. Below the MRTN rate calculation is the “profitable N rate range,” which lists the range of nitrogen application rates over which net economic return is within $1/acre of the MRTN rate. These rates will allow the grower some flexibility in determining nitrogen rates for specific fields. “Net return to N at MRTN rate” displays the economic net return at the MRTN rate. “Percent of maximum yield at MRTN rate” gives the proportion of yield that may be produced at the MRTN rate. In this example, it is estimated that 99 percent of the maximum yield will be produced at the given MRTN rate.

9. Fertilizer-specific information. In this example, we chose anhydrous ammonia as the nitrogen source; therefore, the rate of anhydrous ammonia (pound of product per acre) is given to satisfy the MRTN recommendation. The cost of using this product at the MRTN rate is given in dollars per acre.

10. Graph information. This is a visual representation of the N rate calculations. The gross economic return, net economic return (cost of N fertilizer subtracted from gross economic return), and cost of nitrogen fertilizer is displayed. The MRTN represents the highest point on the net economic return curve with the highlighted portion representing the profitable nitrogen rate range.

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