User’s Guide for the Microsoft Excel Economic Based Nitrogen Rate Calculator
Robert Mullen, Maurice Watson, Ed Lentz, and Greg LaBarge
The new Economic Based Nitrogen Rate Calculator can be downloaded from the web at
http://agcrops.osu.edu/fertility/. Once the program has been downloaded, you can edit the ‘Corn
price’ and ‘N cost’ parameters to identify the economic optimum N rate and the agronomic risk
associated with that rate of nitrogen. The information provided below will provide you with
additional information about the Excel program and help you understand how to use it.
Changing the Parameters to Meet Your Information
Step 1. The first option to consider is the previous crop which can be located on the left hand
side of the spreadsheet (Figure 1). It is a drop down menu box, so to change the previous crop
click on the down arrow located at the edge of box. This should reveal the different options.
Select the appropriate previous crop and proceed to step 2.
Figure 1. Previous crop options that can be selected from a drop down menu (circled in red).
Step 2. The next step is to identify the cost in dollars per pound of the nitrogen source you will
be applying. Like the previous step, the different sources of nitrogen are located in a drop down
menu box. Select the correct of form of nitrogen and enter the price per ton in the yellow box
labeled ‘Material cost’. The nitrogen price per pound is automatically calculated in the cell
labeled ‘N price’ (light green background) for the material you selected and the price per ton you
entered (Figure 2). Proceed to step 3.
Figure 2. Fertilizer material and material cost parameters that can be altered to calculate the
price of the material in dollars per pound of nitrogen (circled in red).
Step 3. The only other step involves altering the ‘Corn price’ and ‘N cost’ to provide the
economic nitrogen rate recommendations (Figure 3). To enter the data simply click on the cell
labeled ‘Corn price’ or ‘N cost’ (yellow background) and change the number to the correct value.
If you had the price per pound calculated in this Excel spreadsheet on the left (Step 2) you need
to type in the N price into the ‘N cost’ cell – THE EXCEL SPREADSHEET DOES NOT PULL
THE VALUE INTO THIS CELL AUTOMATICALLY.
Figure 3. Corn price and nitrogen cost parameters that can be altered to generate the economic
recommendations (circled in red).
Evaluating the Recommendation
Once you have entered in the corn price and nitrogen cost, the cells below titled ‘Lowest
recommended N rate’, ‘Maximum return to nitrogen rate’, and ‘Highest recommended N rate’
(light blue boxes) will provide you with the economic recommendations based on an average
response curve (Figure 4).
Figure 4. Range of economic nitrogen recommendations based on corn price and nitrogen cost
(circled in red).
Additional information is provided to allow you to evaluate the agronomic risk, as it relates to
yield, of the different nitrogen rate recommendations (Figure 5). The lower the recommended
nitrogen rate, the higher the agronomic risk associated with that rate. The risk for each
recommended nitrogen rate is located below the recommendation itself (green cells). A value of
100 indicates little risk of yield loss due to nitrogen deficiency, so as the values approach 100 the
lower the risk.
Figure 5. Agronomic risk of the recommended nitrogen rate (circled in red).
An additional green cell is provided that displays the agronomic rate of nitrogen needed to
ensure nitrogen is not limiting based on Ohio State University research (Figure 6). This cell is
not calculated based on economic parameters. It is simply the highest rate of nitrogen needed to
achieve 95% of maximum yield 100% of the time.
Figure 6. Nitrogen rate necessary to achieve 95% of max yield 100% of the time not
considering economic parameters (circled in red).
Understanding the Graphical Representation of the Data
Below the rate recommendations and risk information is a graphical representation of the data
used to calculate the economic recommendations (Figure 7). The red line represents the average
response of corn to applied nitrogen fertilizer based on Ohio State University research. The
average response line does change as the previous crop changes (Step 1). The blue line
represents the gross return generated by application of nitrogen fertilizer at the entered ‘Corn
price’. Gross return is calculated by multiplying the yield at each nitrogen rate times the corn
price. The yellow line represents the nitrogen cost based on the value provided in the ‘N cost’
cell. The green line represents the net return to nitrogen based on the economic information
provided. Net return is calculated by subtracting the nitrogen cost from the gross return (blue
line minus yellow line makes green line).
Figure 7. Graphical representation of the information used to compute the economic range of
nitrogen recommendations.