Iowa State University Extension and Outreach and the Iowa Department of Agriculture and Land Stewardship have developed the Corn Nitrogen Rate Calculator to help farmers find the maximum return on nitrogen fertilizer applications.

The Corn Nitrogen Rate Calculator is an online tool that can be rapidly updated to allow for changing hybrid genetics, rotations and climatic conditions. The calculator database was updated with 2011 response data and now contains 214 trials for corn following soybeans and 111 trials for corn following corn rotations.

“Having adequate nitrogen available is critical for corn production, but given the high prices for fertilizer it is important for farmers to determine the right amount that is needed on their crops,” Iowa Secretary of Agriculture Bill Northey says. “Every farmer wants to make sure plants have the fertilizer they need while not over applying, so this calculator is a great tool.”

The calculator allows farmers to compare up to five price ratios – pricing options for nitrogen and corn. Farmers can then reach out to their local fertilizer suppliers to find current fertilizer prices. The calculator lets farmers determine the optimal rate of application based on up to four different corn prices.

“Nitrogen rates determined by the calculator are the total fertilization amounts for each rotation, there is no need to further adjust the rate for previous crop,” says John Sawyer, soil fertility and nutrient management specialist with Iowa State University Extension and Outreach.

Sawyer reminds farmers they should also wait until soil temperatures remain below 50 F before applying anhydrous ammonia (NH3) fertilizer this fall. A statewide real-time soil temperature data map is maintained by ISU Extension and Outreach at can be used by agricultural retailers and farmers to determine when fall nitrogen applications are appropriate.

The Corn Nitrogen Rate Calculator can be found at