Implications of High N Fertilizer Prices on Corn N Fertilizer Recommendations

By Steve Culman

Nitrogen fertilizer is a major cost in corn production and is a big lever that drives yield. However, not every pound of N fertilizer yields the same return on investment. The first several dozen pounds applied to a corn crop yields large returns in grain, with subsequent pounds still offering returns, but not as effective as before. As N fertilizer rates approach what would be typically applied to corn (150 – 200 lbs N/acre), each additional pound returns less and less and eventually reaches a point where the small increases in grain yield does not pay for the additional pound of N fertilizer applied.

This is not a hypothetical. It’s the normal. It’s what we see year after year in the majority of N rate trials we run across the state. And that’s why Land Grant Universities in the Midwest have universally adopted an economic model to N fertilizer rates in corn. It’s called the maximum return to nitrogen (MRTN) because it seeks to do just this, provide a rate where you will get the greatest return to your N investment and therefore grow the most profitable corn possible.

So what is the magic peak where adding an additional pound of N fertilizer doesn’t pay for itself? It depends of course! It depends on the current price of corn grain and N fertilizer. As fertilizer prices increase, the peak comes at lower N rates. But as grain prices increase, the peak comes at higher N rates. Both fertilizer and grain prices are higher than they’ve been in some time, so they work against each other in terms of increasing or decreasing the N fertilizer recommended rate.

Table 1 shows the price of nitrogen fertilizer at various costs per pound and the equivalent per ton price of two familiar nitrogen sources used in Ohio. Table 2 shows Ohio recommended nitrogen rate for corn following soybean at various price combinations for corn and nitrogen. First, select the nitrogen price (column), then select the corn price (row). The cell where the selections intersect is the recommended nitrogen rate.

With current fertilizer and grain prices, our recommended corn N rates are 15-20 lbs/acre less this year than they have been in years past. This might cause some growers to pause and consider if this is really a good idea, but if you want to maximize your profitability, lower rates will ensure you’re not applying additional fertilizer that isn’t yielding a high enough return to pay for itself.

Table 1. Price per Ton of Anhydrous and 28% UAN at Various Price per Pound of Nitrogen Fertilizer Costs.

Table 2. Ohio MRTN recommended Nitrogen Rates (lbs nitrogen/acre) for Corn following Soybean based on the Price of Corn Grain and Nitrogen Fertilizer.