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Don't Worry About P and K Issues in Corn after Corn

Dedicate your time to selecting hybrids instead.

You're likely to experience more problems or at least the potential for more problems if you grow corn after corn. Don't spend your time fretting over things you think might be problems, which really aren't. That's the advice from Bob Nielsen, Purdue University Extension agronomist and corn specialist, and a host of other Purdue Extension specialists who helped him prepare an extensive report on how to minimize potential for yield loss in corn after corn situations.

The report is entitled, "Mitigate the downside risks of corn following corn." It's available at: You can also ask your local Extension educator fro help in securing a hard copy of the bulletin.

The situation that might seem to be a problem, but which most likely isn't, is soil fertility beyond nitrogen, Nielsen notes in the publication. While you will likely need to up N rates as much as 30 to 50 pounds per acre, you may not need to worry about adjusting phosphorus and potassium rates, at least not in the short run. That could be good news, with prices for both potash and phosphate fertilizer soaring right now.

It's fact that corn removes more soil phosphorus and less soil potassium per acre than soybeans, the agronomists note. A 180-bushel corn crop should remove about 67 pound sper acre of Phosphate and 49 pounds of potash, compared to removal of 48 pounds of phosphate and 84 pounds of potash by a 60-bushel per acre soybean crop.

However, based on past research, Nielsen and the team compiling the most recent bulletin determined that a one-time move to second-year corn will have negligible effects on P and K soil fertility issues. If you stay with continuous corn in the same field over a number of years instead of returning to corn and soybean rotations at some point, monitoring both phosphorus and potassium levels through soil tests becomes more critical. However, maintaining good soil testing programs is good advice for anyone, the agronomists say.

Eventually, it might be necessary to adjust phosphorus and potassium levels if you keep a field in corn after corn, vs. what you might do in terms of fertilization programs if it was in a corn/soybean rotation. But in the short run, you've likely got more important things to consider if you want to minimize any possible yield drag from growing corn after corn, and keep profits at a healthy level.

Chief amongst those is making sure you establish good stands, Nielsen says. One of the keys to good stand establishment in corn after corn is selecting hybrids with superior seedling vigor ratings. Ask your seedsman for honest opinions on which hybrids can handle the more challenging corn-after-corn environment best.

TAGS: USDA Extension
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