Determining your ideal nitrogen application rate can be challenging. The two most highly recommended methods for determining your Nitrogen rate are the Yield Goal Method and the Economic Optimum Method. Farmers can also check how specific varieties perform at varying levels of nitrogen.
YIELD GOAL METHOD
For years, the Yield Goal method was the primary way of determining N rates. This method used your three- to five- year average yield and multiplied this figure by anywhere from 1 to 3 lbs of N/acre to determine
the rate you should apply.
However, a tremendous amount of research over the last couple of decades has indicated that there is, in fact, no relationship between N rate and yield. Researchers across the country have found that in high-yielding soils and climates, significantly less N can lead to high yields, while at the same time in low-performing soils and climates, yield tends to be mediocre even when high amounts of N are used.
WHAT’S THE BOTTOM LINE?
Because your highest performing fields need less nitrogen, and additional N will go to waste on your lowest performing fields, it may make more sense to determine your N rate based on the price of nitrogen and commodity corn prices than on a yield goal.
ECONOMIC OPTIMUM METHOD
The Economic Optimum Method of determining N rates takes a different approach. Rather than focusing on a standard yield goal for each field (that may or may not be realistic), it focuses on the price of your N product, the price at which you could sell your corn, and any nitrogen credits that you might have built up in the soil based on your crop rotation, tillage, or past fertility practices. By focusing on the profitability of N use rather than simply maximizing yield, the Economic Optimum method allows you to accurately evalute the potential tradeoff between cost and yield.
UNDERSTANDING THE ECONOMIC OPTIMUM METHOD
There is a lot of jargon and acronyms used by researchers and agronomists when discussing the economic optimum method. But what exactly is your Economically Optimal Nitrogen Rate (EONR) or your maximum return to N?
If your EONR is 160lbs/A, the cost of putting the 161st pound of nitrogen on your eld costs more than the yield bene t it would contribute. For example, if that extra pound costs you $4.00, but will only yield one additional bushel at $3.50, the extra pound of N didn’t make sense, in fact it’s cost you $0.50. EONR and Maximum Return To N, or MRTN, are generally used interchangably, and both refer to an N rate which maximizes your profit per acre rather than yield.
EONR is the core of the new way of thinking about N application rates. The reality is that the natural system by which nitrogen is accessed, used, processed, and released by plants and bacteria under varying conditions is not well enough understood for there to be any kind of magic answers around how much nitrogen is the perfect amount. What you can know is the price of corn and the cost of the N product, and you have a good idea of the likely result of each additional quantity of N used. Knowing these pieces of information allows you to maximize pro tability instead of yield and better control N costs.
There are many different tools you can use to determine your economic optimum, you can also check how specific hybrids or varieties perform at varying level of nitrogen.