How Much Can We Reduce Corn Nitrogen Because of Higher Prices or Short Supply?

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Nitrogen (N) prices are at or near $1.00 per pound. Many still assume that application of 1. 0 lb./ac of N results in 1.0 bu/ac of corn. If so, for 150 bu/ac corn yield that received a total of 150 lbs./ac of N, then $1 from every bushel sold is needed from the targeted corn price to pay for nitrogen. The balance of the target price will have to pay for other inputs. Let that sink in. Since N is indeed a critical input, one must apply sufficient N, but not excessive N. Economic consideration must be involved when determining input more in 2022 than in years past. This begs the question. “How much N do we really need?”

To determine this answer, first one must realize that nitrogen use efficiency for corn hybrids is so improved that many can utilize N much more efficiently than our standard of 1.0 lbs. of N needed to make 1.0 bu/ac corn. Whether you examine NC Corn Yield Contest data, NCSU research data, Midwest data, or other sources, one will quickly notes that nitrogen use efficiency (NUE) has greatly improved. So, if one is still applying 1.0 lb./ac N for each bushel produced, one can indeed reduce N rates without negatively impacting yield.

Recalling that N prices are about $1/lb. and a 1:1 relationship between pounds of N applied and bushels created, one can reduce N cost by 20% yet maintain yield simply by adjusting to the NUE of 0.8. Put another way, reducing N only slightly does not impact yield yet adds another $0.20/bu to the price without the worry and waiting for the market to increase!

Additional data can be examined using data from the work of Drs. Rob Austin and Deanna Osmond NCSU Crop & Soil Science Department, that compared grower N rates to rates 25% more and less than the grower rate over a 5-year period. The data is shown below.

Rate                                                                Average Yield (bu/ac)            NUE    

25% Below Grower Rate = 132 lbs./ac N                    160                              .83

Grower Rate + 174 lbs./ac N                                       167                              1.04

25% Above Grower Rate = 215 lbs./ac                       172                              1.25

As one can see, there was little yield difference between the 25% lower N Rate and the Grower N Rate. Yes, the 25% Above Grower Rate Is indeed the highest but it took 41 more gallons of N than the Grower Rate and 83 more gallons than the 25% Below Grower Rate. At about $1 per pound of N, that is $41-$83/acre savings available. Too, consider that should one have used the higher rate of 215 lbs./ac N compared to the Grower Rate of 174 lbs./ac N, the difference is only 5 bu/ac corn yield. As such,  the $41 additional money spent on N means those few extra bushels must be sold at $8.20/bu to pay for the additional N input!

Lastly, consider the best profit gained by the N rate. To examine this simply divide the yield by the nitrogen price rate for the given rate. The 25% Below Grower Rate (167/132) results in in 1.2 or 20% profit for each dollar spent on nitrogen. The Grower Rate (167/174) resulted in 0.95, a loss of 5% for each dollar spent on N. The 25% above N (172/215) shows greater loss of 20% for each dollar spent on N.

This type of data is reflected in this area too. Data from replicated test within Craven, Pamlico and Onslow counties in  2021 is shown below. Note that data from all counties show no statistical difference between the Grower N rate and 25% lower N rate. In fact, only results from Pamlico County show a statistical difference between the Grower and 25% Above Grower Rate of N.

Bar graph of corn yield at three nitrogen rates and there locationsYes, numerically there is a difference but we should believe the statistical test. If you are one that doesn’t, then examine this data using the same economic evaluation as previously. The rates of N application averaged 114, 153 and 192 lbs./ac for the 25% Below, Grower Rate, and 25% Above N rates. Average yield was 172, 184, and 199 bu/ac, respectively. Dividing the yield by price of N for the given rate results in 1.52 for the 25% lower N rate, 1.21 for the Grower Rate, and 1.04 for the 25% Above Grower N rate. In this case, results are all positive but the difference in profit from this input is 48% between the lowest and highest return.

These analysis assume that N rates are independent of other inputs. They are not and we realize this. However, these data show that the NC Realistic Yield Expectation (NC RYE) N rates are targeted for optimum yield and profit. If one is at or near this rate, then one is making good management decisions. Having thusly said, should prices continue to increase or N become in short supply, realize that lowering rates 25% below the NC RYE rate still provides outstanding yield. In fact, often 25% less than the NC RYE is the most profitable!

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