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Preliminary Observations Raise Questions About Nitrogen Rate

Optimum agronomic vs. economic rate needs hard look.

Final numbers aren't in yet from the nitrogen-trial plot on John Kretzmeier's farm in White County. It's an important plot because Purdue University agronomists Bob Nielsen and Jim Camberato helped design it to answer questions about optimum N rates in Indiana. They are also now harvesting plots at either key locations, some of them at Purdue outlying farms and some elsewhere, to help answer this question.

The White County plot was harvested about 10 days ago. Speaking only armed with preliminary numbers, not final data, Nielsen was hesitant to crawl too far out onto a limb for fear the real numbers might later cut the limb off. But here's what he's thinking in relation to that plot so far.

"Our yields there were in the 190 average range, similar to last season," he notes. "In '06 with more rain the optimum rate for yield response seemed to be not much over 100 pounds per acre there, although it was considerably higher in plots on the eastern side of Indiana. It appears it's going to be somewhat higher at the White County site this year. We may end up around 140 pounds total N applied as the key rate here."

From experiments at the Southeast Purdue Ag center near Butlerville in Jennings County, on completely different soils, it appears that the gap between best agronomic rate and maximum economic rate may be quite large. That plot was harvested just a few days ago. Early indications looking through the data indicates that the gap could be as wide as 20-30 bushels per acre. Top agronomic rate is where yields top out. Top or maximum economic application rate of nitrogen is the point at which it doesn't pay to apply the next pound in terms of expected yield response to that unit of N, and extra revenue from the amount of corn produced.

"What's making the difference right now is 50 cent per pound nitrogen," Nielsen says. "That's roughly the price of actual pound of N if you're applying liquid 28% N."

While $3 per bushel is a healthy price, and the figure Nielsen was using in his rough calculations, it still does not totally offset 50 cent per pound N. "The gap would narrow if corn was higher priced or N was cheaper," he says.

Indications from insiders are that N is not likely to get cheaper as the season progresses into next spring. If you believe some marketing consultants, corn could rally back to higher prices during the winter or into next spring, as it attempts to buy the acres end-users need for '08 needs.

Stay tuned for the final word on these and other plots as Nielsen completes harvest this fall.

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