What Are the Yield and Economic Risks of Underapplying Nitrogen in Corn?

With supply chain disruptions and global events over the past year, one question floating around winter 2022 has been “if we aren’t 100% certain today that we can source all the nitrogen (N) fertilizer we normally would, what are the risks if we don’t apply our normal N program in corn?”.

If you are in the uncertainty camp, perhaps you are weighing whether:

• corn acres stay at original intentions, but under the risk of uncertain final N supply and rates
• corn acres are reduced as a hedge to ensure that acres planted will have relatively normal N supply and rates.

Yield Risks for Underapplying N

What are the risks for underapplying N? To provide some insight, I will use a 2011-2014 N response dataset from 15 trials conducted on-farm across parts of Southern Ontario by former OMAFRA corn specialist Greg Stewart.

These N response curves (Fig. 1) include the Most Economic Rate of Nitrogen (MERN) for what might represent a:

• 10-year average cost/price scenario (green dot, $5.00/bu corn and $0.60/lb-N fertilizer)
• 2022 cost/price scenario (red circle, $6.75/bu corn and $1.20/lb-N fertilizer)

For more background on MERN, see the article “Understanding MERN (Most Economic Rate of Nitrogen) for Corn” (Rosser, 2022b).

Yield risks for underapplying N in this dataset can be made by comparing yield loss for these curves as N is shorted below MERN. Since most on-farm N rates are likely selected to not limit yields in most years, I will compare yield declines as N rates are shorted relative to the longer term 10-year average MERN (green dots).