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Nitrogen application dissected

February 26, 2008
By Vicki Johnson, agnews@advertiser-tribune.com
GIBSONBURG — Optimal nitrogen application rates, pest and disease control were the main topics during Northern Ohio Crops Day recently at Ole Zim’s Wagon Shed.

The day was hosted by Ohio State University Extension educators in Seneca and surrounding counties, which enables them to provide more information than each hosting separate agronomy days.

Ed Lentz, OSU crops specialist and Extension educator in Seneca County, talked about nitrogen recommendations for wheat.

He said the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa still are good recommendations if the amount of nitrogen put on in the fall is deducted from the total.

Too much nitrogen can be expensive and bad for the environment.

“It’s no longer cheap insurance,” he said.

Lentz said nitrogen should be put on during the stem extension phase of growth, rather than earlier in the season.

“Most of this nitrogen isn’t needed until May 1, or even June, when the bulk of this nitrogen is being used,” he said.

According to studies he conducted at the Ohio Agricultural Research and Development Center’s Northwest Agricultural Research Station near Hoytville, Lentz said an average yield of 90 bushels per acre required 80 pounds of nitrogen. He added the nitrogen during four different stages and found the early stem elongation stage was best, as opposed to putting it on before it greens in the spring, shortly after it is coming out of winter dormancy or later in its life cycle.

“We get really nervous when people put on nitrogen early,” he said. “There’s no advantage to you for putting it on early. Wait until (at least) greenup.”

He suggested the best time is late March through the end of April.

If the price is equal for all types of nitrogen, Lentz said recommended producers choose the best type for environmental conditions and the potential for nitrogen loss.

He also said adding sulphur may be beneficial to sandy soils low in organic matter.

Robert Mullen, fertility management specialist with OARDC’s Wooster office, gave nitrogen recommendations for corn that are lower than those traditionally recommended.

“The basic idea (traditionally) is as my maximum yield increases, the nitrogen rate I need to apply to achieve that yield should be increasing, too,” he said.

“But as yield rates increase, it doesn’t necessarily translate into higher nitrogen rates,” he said. “That flies directly in the face of what we have historically and traditionally said. The rules of the game have changed considerably.”

Mullen said new nitrogen recommendations for corn are based on a range.

“It’s a balance game that we’re trying to play,” he said.

Producers must know the point where economic risk outweighs agronomic risk, he said.

Lots of new data in last two years show today’s new hybrids and changes in rotation may be changing the nitrogen needs.

“It doesn’t justify a yield-based approach,” he said.

Differences in weather-related mineralization of nitrogen make a difference in the amount of nitrogen available to the plants.

“It’s a pretty complex system we’re dealing with in production agriculture,” he said. “Economic reality today is dramatically different than it has ever been.”

Dennis Mills, a plant pathologist at OARDC’s Wooster office, talked about managing crop diseases.

“Don’t routinely apply fungicide,” he said. “It’s a tool to be used and used smartly.”

He recommended the best methods as planting resistant varieties, rotating crops and tilling ground to destroy crop residues if a problem becomes unmanageable.

“Those are the tools we have to use, and they really don’t cost you that much,” he said.

Foliar fungicides can be an option for corn when needed, he said.

“Fungicides can be used, but they don’t work on everything out there,” he said.

Mills said corn can be affected by disease a lot more quickly in corn-after-corn fields, rather than a corn-after-soybeans rotation.

If fungicides are used, Mills said producers must know for what they are spraying.

Know the hybrid susceptibility,” he said. “Know the disease in question. Apply fungicide at the right time. And know the threshold levels.”

He suggested asking whether spraying is economically beneficial.

“Spraying when there’s low levels of disease takes money out of your pocket and doesn’t put any in,” he said.

Andy Michel, OSU assistant professor of entomology, gave an update on insects.

“One area we’re concerned with is first-year corn rootworm,” Michel said.

He said rootworm is adapting and laying its eggs in corn fields, which makes crop rotation more important than ever.

The pest started in 1990s in central Illinois and has been spreading.

“This is the second year we’ve seen consistently high levels (in western Ohio) and we think some fields might need treatment this spring,” he said.

Michel said western bean cutworm is spreading eastward, but is not yet a problem in Ohio.

“The total number of moths we caught in Ohio was only five last summer,” he said.

Soybean aphid should not be too much of a problem during the coming growing season, he said, even though it usually follows a two-year cycle and 2007 wasn’t a bad year either.

“This winter it doesn’t seem to be overwintering well,” he said. “We’re predicting it will continue to follow the low-year, high-year cycle. There will probably be low aphids this year, following the same pattern.

“Everything was in line for a bad season in 2007,” he said.

But he said he suspects last year’s early-April freeze killed most of them. “This probably resulted in a low population for the rest of the summer,” he said.

Michel said a dry season could cause a problem with two-spotted spider mites.
 
 

 

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