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Here’s a Corn-On-Corn N Sweet Spot

215 pounds per acre of N was the optimum N rate on south-central Iowa Beck's Hybrids site.

Those of you who struggle with hardscrabble clay or rock-pocked soils would die for the deep, rich black soils oozing with 4% to 5% organic matter on which the Beck’s Hybrids Practical Farm Research site near Colfax, Iowa, is located. Corn planted on these soils can take advantage of generous nitrogen applications.

Still, there’s a limit. Beck’s research found the optimal N rate for corn-on-corn is around 215 pounds per acre on this farm, says Wade Kent, a field agronomist for Beck’s Hybrids. Kent presented Beck’s Hybrids’ findings at the site’s first Iowa Field Show this week.

Corn with N applications of 125 pounds per acre showed the telltale sign of leaf firing that signals N deficiency. But there isn’t an economic edge for rates as high as 250 pounds per acre, either, he says.

Corn-on-corn needs more nitrogen because there is typically a yield lag compared with corn following soybeans of 10% to 15%. Although there have been management strategies where the yield discrepancy narrows between 5% and 8%, corn-on-corn does need more N, says Kent. That’s particularly true as corn yields steadily increase each year at the clip of around 1.5 bushels per year.

Adding N Can Help Soybeans, Too

Surprisingly, soybeans need N, too. Soybeans require 4 to 5 pounds of N per bushel of soybeans, says Chad Kalaher, Beck’s Hybrids field agronomist.

Soybeans manufacture much N via nodulation. Still, N applications have benefitted soybean return on investment (ROI).

Beck’s researchers added 30 pounds per acre of UAN on soybeans in a two-year trial. Stage and the per-acre return on investment (ROI) of the fertilizer application were as follows:

  • Preplant incorporated: $43.07
  • V6 (sixth trifoliate) sidedressing: $29.05
  • Broadcast application between R3 and R4 stages (podding): $24.15

On average, this tallied into about a $32-per-acre return from the N applications.

There’s the thinking that adding N fertilizer will make soybeans lazy and not nodulate. But Kalaher says that hasn’t surfaced in Beck’s Hybrids tests.

“Applying nitrogen to soybeans is one way to break through yield barriers,” he says.

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