Small Town News

Watch corn fields for nitrogen deficiency

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Many South Dakota corn growers and crop advisers are reporting late season nitrogen deficiency in their fields, and potential yield losses are a concern.

That's according to South Dakota State University plant science professor Ron Gelderman, who said telltale signs of the deficiency after tasseling include "leaf firing." "It shows up as yellowing on the lower leaves, and the yellowing develops at the tip of the lowest leaf and works its way down the midrib to the stalk," said Gelderman. "This yellow area will eventually die and is referred to as 'leaf firing.' As the deficiency becomes more severe, the firing moves up the plant and affects leaves located higher in the plant."

Gelderman said these symptoms are jiot to be confused with the yellow plants that we see in low areas that may have been flooded earlier in the year. He said the reported leaf firings seen now are on well-drained, highly productive areas of the field.

"This year it seems there is more extensive leaf firing and it is occurring on leaves higher on the plant," Gelderman said. "This might be due to the fact nitrogen fertilizer was very expensive this past winter and spring when many growers were deciding on a nitrogen application rate. Some growers reduced their applications below the recommended rate to save some input costs."

Another reason Gelderman said this problem is occurring is because of an excellent growing season so far.

"Many growers report having the best crop potential they remember at this time in the season, and the extra plant growth simply requires more nitrogen," he said.

Gelderman cites an example with a grower planning for a 150 bushel per acre yield goal.

"Increased rainfall has provided for a plant growth potential of possibly 200 bushels an acre, so the plant may not have adequate nitrogen, resulting in the deficiency," Gelderman said. "As a corn plant matures, it is common for the lower, oldest leaves to show nitrogen deficiency, because the plant recycles nutrients from these leaves that are not contributing much to the plant's growth."

Gelderman said producers who wonder how high on the plant that this firing can take place and not reduce yield can look at completed research for answers.

"Work from Iowa State University that was confirmed by research from Perm State University indicates that if the firing has not reached the leaf below the primary ear leaf, there is a 90 percent chance that yield was not reduced," he said. "This research was done at the dough-to-dent-time corn-growth stage."

As they harvest, Gelderman suggested that producer note if harvested yields meet yield goal expectations.

"In many seasons with good growing conditions, a field will produce more corn than we had planned," he said. "The reason is that excellent growing conditions also provide good soil microbe activity. The microbes convert non-plant available N that is in old plant residue or soil organic matter to readily available plant-usable nitrogen. The result is we have more N available to our corn plant than we expected in the spring."

Gelderman said this extra nitrogen will support the additional plant growth and increased yields.

Once harvest is complete, Gelderman recommends producers take a 2-foot nitrate-nitrogen soil test to determine carryover available soil nitrogen levels. Typical N carryover after corn is from 50 to 70 pounds an acre.

"If you have met or exceeded yield goals, it would not be surprising to see carryover levels lower than average," said Gelderman. "However, if we have met or exceeded yield goals and have high-er-than-average carryover nitrogen levels, we may be over-applying nitrogen. Checking these carryover levels is another way to fine-tune your N recommendations and save on input costs."

Contact the county extension educator for soil-sampling information, or call the SDSU Soil Testing Lab at (605) 688-4770.



Copyright 2009 Hutchinson Herald, Menno, South Dakota. All Rights Reserved. This content, including derivations, may not be stored or distributed in any manner, disseminated, published, broadcast, rewritten or reproduced without express, written consent from SmallTownPapers, Inc.

© 2009 Hutchinson Herald Menno, South Dakota. All Rights Reserved. This content, including derivations, may not be stored or distributed in any manner, disseminated, published, broadcast, rewritten or reproduced without express, written consent from DAS.

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