January 7, 2016
The maximum agronomic corn yield is the top yield you can achieve if you're just concerned about yield and not price of inputs. The maximum economic yield is the highest yield you can achieve before the next bushel of yield doesn't cover the last unit of inputs, typically fertilizer, needed to reach that yield. In other words, it's where you make the most return for gross revenue minus input costs.
Right rate: There is a maximum rate of fertilizer to apply per acre if you're trying to maximize returns and not yield.
Why is the difference important, especially in 2016? The difference in these two rates represents potential cost savings. As with any cost item, it's important to compare potential benefit of each additional unit of input related to yield and output price, and the cost of each unit of fertilizer.
Using the Purdue cost and return budget, each 10-pound increment in nitrogen represents a cost of $4.28 per acre for corn. Purdue agronomist, Jim Camberato, notes that for west central and southwest Indiana, the average agronomic optimum N rate is 183 lbs. of N per acre.
Using an N cost of $0.40, the economic optimum N rate varies from 156 lbs. per acre for a corn price of $2.50 to 170 lbs. per acre for a corn price of $5. As corn prices go up, the amount of N you can apply to reach maximum economic yield also increases.
In addition to N rates, nitrogen costs are impacted by application timing, split applications, use of starter fertilizer, N loss, weather and numerous other factors. Again, when analyzing changes to N management it's important to compare the benefits of the change to the costs associated with the change.
More information pertaining to cost items for corn, soybeans, and wheat can be found on the web site for the Center for Commercial Agriculture.
Langemeier is director of cropping systems for Purdue University's Center for Commercial Agriculture. He writes from West Lafayette.
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