No magic rate for nitrogen

I convinced my dad to go from 175 to 200 pounds of total nitrogen on corn in ’23 since corn prices are solid. Then he saw results from an on-farm test someone did nearby last year. It showed no yield benefit above 180 pounds N. Now he’s balking at 200 pounds. Who is right?
The Indiana certified crop adviser panel answering this question includes Gene Flaningam, agronomist with Flaningam Ag Consulting LLC, Vincennes; Greg Kneubuhler, agronomist with G&K Concepts Inc., Harlan; Troy Jenkins, agronomist with Ceres Solutions and 2022 CCA of the Year; and Dan Quinn, Purdue Extension corn specialist.
Flaningam: Nitrogen management on corn varies by soil productivity, drainage, rainfall, nitrogen cost and grain prices. Look at the farm’s recent productivity history and adjust nitrogen rates. Then look at your expected cost per unit of nitrogen vs. the value per bushel of corn.
Kneubuhler: The correct rate of nitrogen is the million-dollar question each year. It really comes down to recoverability and efficiency on your farms. Mother Nature drives a lot of that final number each year. Over the past 15 years, we have conducted hundreds of side-by-side nitrogen tests just like the on-farm trial mentioned. Of course, every year is different, but the number that seemed to rise to the top in our trials for “right rate” of nitrogen tended to be around 180 pounds per acre. A lot of factors drive this rate, from soil balance to drainage to stand establishment to calcium levels. Form of nitrogen also has an impact on rates. If you’re using ammonia vs. UAN, that drives my decision to determine rates.
But, in summary, you are really both right: 175 pounds can end up being enough, but also the 200-pound rate can offer big paybacks under higher-yield environments and/or adverse weather.
Jenkins: Nitrogen is the most variable nutrient in corn production. There is no exact amount of nitrogen for every year. In research studies at Purdue, the agronomic optimum nitrogen rate from 2006 to 2015 was 197 pounds per acre, ranging from 130 to 262. This was more than a 100-pound-per-acre difference over the 10 years. Hybrid response to N, application timing, denitrification or leaching, soil temperature, soil organic matter, N mineralization and use of nitrification inhibitors effect nitrogen efficiency.
In short, there is no one exact correct rate. Using split-nitrogen applications, in-field pre-sidedress N testing, nitrification inhibitors and the Corn Nitrogen Rate Calculator based on economic optimum nitrogen rate may help in nitrogen rate decisions.
Quinn: This is hard to answer because available nitrogen is so difficult to predict. In one specific year or one specific field right next door, one person can be closer to being right, and in the next year or next field, the other person could be right. It’s difficult to predict available nitrogen both released from the soil or lost from the environment in one year. Each are environmentally controlled.
Use Purdue University nitrogen recommendations. Backed by years of data, they can help you get close to optimum and economic nitrogen rates for your location. It’s always worthwhile to try strips of different nitrogen rates within fields each year to get a better sense of optimum nitrogen rate.