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Deal or no deal: Finding the right nitrogen rate

One of the largest investments in a corn crop is the nitrogen (N) application, and many farmers will be sidedressing their corn soon. Especially with this year’s profit outlook, it is important to carefully consider how much N to apply. Deciding on the correct N rate can be a lot like playing the game “Deal or no deal.”

“Deal or no deal” was a TV game show that aired a few years ago. The game consisted of a series of 26 cases, each containing a different amount of money ranging from $0.01 to $1,000,000. A contestant would select a case at random, and then play the game to reveal how much money was in their case, or try to sell their case for more than it was worth.

Each corn field will require a certain amount of N to reach its maximum yield potential. However, that ideal rate is a lot like the dollar value in the contestant’s case — it isn’t known until the end of the game (harvest). So we have to use the tools that we have available to make our best guess as to what that ideal rate will be when we make the application.

The average is usually a good place to start. It’s easy to take the value of all the cases in the game and determine that, on average, a contestant will take home $131,477.54. Iowa State University, in association with The Ohio State University, developed an online calculator that estimates the maximum return to N rate (the rate at which you achieve maximum yield per dollar of N invested). To use the tool, go to http://cnrc.agron.iastate.edu/, select Ohio, and enter your cost of N along with your value of corn. The tool uses multiple years of university studies to provide the N rate which, on average, will be most profitable for your farm. However, this average could still be quite different than the actual ideal rate that a crop needs, just like a contestant wouldn’t want to give up the $1,000,000 case for the average case value.

In the game of “Deal or no deal,” the potential value of the contestant’s case is narrowed down as the game progresses and they open other cases, eliminating the possibilities of what might be in their own case. In farming, each passing day is like opening another case. Each day’s weather will tell a little bit more about how much N is available to the crop. If May and June bring a lot of sunny days and just enough rainfall in small increments, then any early-applied N is most likely still available to the crop. Or, if a field experiences several heavy rainfall events, there is a good chance that some of the N has been lost. Split-applying N or delaying an application can put more weather behind you when making the application, therefore narrowing the range that that final ideal rate will fall in.

Periodically throughout the game show, the banker will offer to buy the contestant’s case by analyzing the current situation in the game. While neither the contestant nor the banker knows exactly what is in the case, the banker’s offer gives the contestant an idea of what the case is worth. Farmers can use tools in a similar way to estimate how much N their crop will need based on the current conditions. Using a Pre-sidedress Soil Nitrate Test (PSNT) or other similar test can help you know how much N is currently in the soil and how much you might need to add to get close to that final ideal rate. This can be especially helpful if you applied some N early, applied manure, or expect to get some N credit from a cover crop.

At some point, the contestant must end the game, either by opening all of the cases or selling to the banker. As a farmer, using the tools available to you such as online calculators, delayed/split applications, and/or soil testing can help you make a better deal when it comes to deciding how much N to apply.

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