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Trimming P & K levels? Be careful

Jeff Caldwell 03/16/2011 @ 3:01pm Multimedia Editor for Agriculture.com and Successful Farming magazine.

Fertilizer prices are climbing, and it may be tempting you to cut back on how much you apply to this year's crop. If you do decide to pull back on how much you put down, take a more surgical approach to avoid losing yield, says one crop adviser.

When Jay Johnson starts working with a new farmer customer, the Beaman, Iowa-based crop adviser with Prairie Crop Pro-Tech says he's noticed a common theme when he starts pulling soil tests. "I see a lot more variability with potash levels, for example. They'll be very low," Johnson says.

He suspects farmers are doing a good job of managing crop nutrients like phosphorus (P) and potassium (K), but that they're "easy to lose" on some acres. "I've always been using more than university recommendations," Johnson says.

But today, with P and K prices again rising, it may be tempting to trim the amount you apply. You can do it, but just make sure you're not already at or near the "maintenance limit," under which your crop could start to suffer.

"In fields with high P and K soil test levels, P and K fertilizer additions often can be eliminated for at least a couple of years to offset high P and K fertilizer prices," says Purdue University agronomist Jim Camberato. "When soil test P and K levels fall below the maintenance limit, regular fertilizer additions are recommended to keep soil test P and K levels in the maintenance range and to keep nutrient levels sufficient for optimum yield."

If you're just not certain whether you can skip a year of P and K applications, or you simply don't want those nutrient levels to fall in your fields, make sure you don't cut application levels across the board. Take additional soil tests to determine your nutrient needs on the individual field level, then adjust applications accordingly.

"We all make the same recommendations, but then we have customers say they can't afford it all, and some just say they want to put on 50% of the recommended amount across the board," Johnson says. "I still insist on going through and resampling, then putting on that 50% they need in the right places and not the 50% they can get by without."

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