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N.D. Sunflower Fertility Guidelines

Tuesday, February 1, 2011
filed under: Fertility

North Dakota State University’s sunflower fertilization recommendations are, to put it kindly, “well aged.” They were actually developed three decades ago and are long overdue for an update, concedes NDSU soil fertility specialist Dave Franzen. The reason they haven’t been updated more recently is, quite simply, a matter of limited human resources — especially when spread across some two dozen major and minor crops for which NDSU offers fertilizer recommendation tables and equations.

So the question then becomes, ‘Do the current sunflower recommendations still adequately serve North Dakota sunflower producers?’ Given the new generations of higher-yielding hybrids being grown by today’s producers, that’s a subject open to debate. In Franzen’s view, the answer has a two-pronged component.

“I think they’re still doing a reasonable job for the average to slightly above-average producer,” he states. “They’re probably not as good as they should be for the exceptional sunflower producer, however.”

Franzen says one mitigating factor — a “cushion” of sorts when it comes to growers not running short on nitrogen due to any shortcomings of the recommendation formulas — has been “the farmer’s general lack of knowledge of his deep N.” By that he’s referring to quantities of nitrogen that are left unused by preceding wheat or other crops. “That nitrogen is going someplace — usually down to a deeper depth, especially in these wet years. And the sunflower is picking it up.

“That’s a big reason why, in some cases, you’re seeing 3,000-lb sunflower yields even though just enough nitrogen was applied to support a crop of maybe two-thirds that amount.”

There’s a caveat for 2011 sunflower fields, however. “We’re coming off two superb wheat crops — and small grain crops in general,” Franzen points out. “So that deep N probably isn’t there in the amount it used to be. Those 60- to 100-bu spring wheat, durum or barley crops have used up much of what was applied and released. So replenishment of the deep N hasn’t happened.”

For any producer shooting for that high-end 2011 sunflower yield, the bottom-line emphasis obviously is, as always, knowing what you have and providing what you’ll need — i.e., a sound soil test and the addition of adequate applied N. “The exceptional grower who hit 2,500 to 3,000 lbs this past year really needs to focus on his production goal for this coming season — and then fertilize accordingly,” Franzen affirms.

“The real productive grower should be thinking somewhere in the neighborhood of 150 lbs of total known available N from 2’ soil test nitrate, any previous crop N credits and added N.” - Don Lilleboe
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