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Recent Rains May Flush Carryover N

April 18, 2013
By: Davis Michaelsen, Pro Farmer Inputs Monitor Editor

We have discussed the potential for nitrogen carryover this year as a result of last year's drought. Generally, the more it rains, the more nitrogen will need to be replaced in the soil. Last year's chapping end to summer had growers eyeing carryover nitrogen and some may even have cut back on N applications.

But as winter changes to spring, some very wet weather has doused the Corn Belt with locally heavy moisture. March held a surprising shot of snow for northern parts of the Midwest which also contributed to recharging soil moisture. But these precip-rich weather patterns may have also contributed to depleting carryover nitrogen.umbrella 6 l

Peter Scharf from the University of Missouri Division of Plant Sciences has been watching these developments closely. According to research conducted near Columbia, MO, there may not be as much nitrogen left in the soil as there was even just a few weeks ago.

"One sample was taken by Bud Motsinger in Caldwell County. His results came back suggesting that a 30 to 40 lb N/acre credit would be appropriate. This was for a field that received 180 lb N/acre but didn’t yield much. There should have been a lot more N left at harvest than he saw in his recent sample, suggesting that some has been lost.

We took a sample a week ago at our research farm near Columbia in corn that had received 180 lb N/acre and yielded 80 bushels. Figuring 1 lb N per bushel ends up in grain and stover, that would leave 100 lb N/acre unused. What we measured in our soil sample to a depth of 3 feet was similar to what Bud saw, suggesting about a 30 lb N credit."

What Scharf found was that recent moisture has had a dramatic impact on N left in the soil and carryover estimates based on yield were incorrect in light of late winter precipitation. The study was conducted on what Scharf termed, "slowly draining soil". The findings also showed that soil moisture had moved deep into the soil profile to recharge dry subsoil, and took a lot of N with it to a depth beyond the reach of corn roots.

Scharf continues, "I have been telling people that if they’re planting corn after corn (or planted wheat after corn), and their corn yields last year were low, they can probably take a credit for some of the leftover N and cut back rates. I’m now worried about this suggestion--two recent deep soil samples suggest that at this point a credit for last year’s N should be low."

Late season rains are a welcome and timely sight for the drought stricken Midwest, but as the weather changes, so must our approach to the soil profile.

"So if you have taken a credit for last year’s leftover N, or were planning to – PROCEED WITH CAUTION. These results are only from two fields, and other fields are sure to be different, but they suggest that the risk that comes with taking a nitrogen credit is higher than I would have guessed.

For wheat, time is rapidly running out to correct any potential problems. I would suggest quickly scouting any fields where a credit was taken, and getting an additional 30 lb N/acre applied soon to fields where any sign of N deficiency is seen.

For corn fields where a credit was taken and N was applied at a lower-than-normal rate, I suggest the same thing–watch carefully and run some more nitrogen over the field at the first sign of deficiency," Scharf said.

(Click here for the full University of Missouri article.)


Photo credit: 55Laney69 / Foter.com / CC BY

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