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Study Finds Large Difference in Optimum N Rate

Study Finds Large Difference in Optimum N Rate
Corn after corn rate to get good response much higher than after beans.

Results from Practical Research Plots conducted by Beck's Hybrids are showing that it pays to apply more nitrogen for corn after corn than many people have previously recommended. Some farmers claim they're getting good performance with minimal extra N. However, that's not what long-term data shows.

Beck's Hybrids now do practical research plots at four locations: central Indiana (Arcadia), southern Indiana (near Ft. Branch), central Illinois (near Lexington) and southern Illinois, just north of Effingham. While studies are not replicated at each site, some of the studies, including most nitrogen studies, are repeated using the same lay-out design at all locations.

Six year- data gives the biggest indication of how much difference Beck's has found in the need for nitrogen in corn after corn vs. corn after soybeans. However, some of the sites were not up and running when the plots started, so the data includes only fairly recent data for central Illinois and southern Illinois sites.

If nitrogen is 40 cents per pound and corn is $4.25 per bushel, optimum yield in corn after soybeans is just over 175 pounds per acre, Scott Ebelhor says. Ebelhor manages plots at the Ft. Branch location, consisting of more than 80 acres on good soils.

However, if nitrogen increases to 50 cents per pound, the optimum drops to just over 170 pounds per acre. At 60 cents per pound, either due to an increase in anhydrous cost or because you elect to use more expensive N forms, then the optimum rate falls between 165 and 170 pounds per acre of total applied nitrogen.

Various soils types are included in these studies. These findings are relatively similar to those Purdue University have reported for much of Indiana recently, except for east--central Indiana, where required rates to produce the same or even lower yields tend to be higher.

The picture changes when you look at corn after corn, notes Scott Beck, vice president of Beck's Hybrids. At 40 cent per pound N and $4.35 per bushel corn, the optimum rate over the six-year average moves to just over 230 pounds per acre. At 50 cents per pound, its' just over 225 pounds per acre, and at 60 cents per pound the optimum applied rate of N would be 220 pounds per acre.

Making the comparison, the range is 168 to 176 pounds per acre after soybeans, and 220 to 232 pounds per acre after corn. Those are differences of just over 50 pounds per acre for comparative N prices. Many studies in the past have concluded that 30 or 230 to 40 pounds additional N should be sufficient in corn after corn situations.

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