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Could you boost yields and make money by applying N on late-season soybeans?

Tom Bechman 1, Editor, Indiana Prairie Farm

August 5, 2016

2 Min Read

One farmer in Indiana reported a 7-bushel-per-acre yield increase where he applied nitrogen over soybeans late in the reproductive stage a year ago. Other farmers are thinking about trying this. The idea, farmers say, is that supplying nitrogen when bacteria inside nodules slow production should provide a yield kick. Is it a proven practice or a theory?

Right now, Shaun Casteel, Purdue University Extension soybean specialist, says it’s a theory. He’s not aware of any hard scientific proof. Here is how Casteel answered Indiana Prairie Farmer's questions on the topic.

IPF: Does the theory make sense?


Casteel: Let me explain what happens inside the soybean plant. Soybean N fixation peaks around R5, or the first pod stage. It drops thereafter. The period of pod development to seed fill places the highest demands on soybean nutrient needs in terms of uptake and remobilization, as well as photosynthate supply.

IPF: Can you continue?

Casteel: Nitrogen supplementation to boost soybean yield is certainly a mixed bag of results due to multiple factors. Supplying N as fixation supply wanes makes sense provided soybeans are able to take it up without inhibiting the initiation and supply from nodulation and fixation.

IPF: What have you seen in terms of applying nitrogen to soybeans during the season?

Casteel: I agree timing and N source can play into the nature of the soybean yield response. We see positive results one out of three tries when we apply urea plus slow-release urea around the V5 vegetative stage. We chose V5 to early reproductive stage to build the N bank in the leaves for remobilization. The remaining two out of three tries has no yield response. The odds are not in your favor for a blanket, blind application. Our N rates were 30, 60, 90 and 120 pounds per acre. The positive yield results came at any of these rates. Fortunately, the higher N rates did not suppress yields, either.

IPF: Is there a time when you would consider applying nitrogen on soybeans?

Casteel: If field conditions seem to be limiting mineralization of soil organic matter and/or the soil supply is naturally low, then supplemental N may be beneficial. Saturated soils with moderate temperatures, like June into early July in Indiana in 2013, are also candidates for N on soybeans, but it still doesn’t guarantee a yield response. We’re also exploring the yield response in the presence of sulfur from either the soil, or from fertilizer such as ammonium sulfate or thiosulfate.

About the Author(s)

Tom Bechman 1

Editor, Indiana Prairie Farm

Tom Bechman is an important cog in the Farm Progress machinery. In addition to serving as editor of Indiana Prairie Farmer, Tom is nationally known for his coverage of Midwest agronomy, conservation, no-till farming, farm management, farm safety, high-tech farming and personal property tax relief. His byline appears monthly in many of the 18 state and regional farm magazines published by Farm Progress.

"I consider it my responsibility and opportunity as a farm magazine editor to supply useful information that will help today's farm families survive and thrive," the veteran editor says.

Tom graduated from Whiteland (Ind.) High School, earned his B.S. in animal science and agricultural education from Purdue University in 1975 and an M.S. in dairy nutrition two years later. He first joined the magazine as a field editor in 1981 after four years as a vocational agriculture teacher.

Tom enjoys interacting with farm families, university specialists and industry leaders, gathering and sifting through loads of information available in agriculture today. "Whenever I find a new idea or a new thought that could either improve someone's life or their income, I consider it a personal challenge to discover how to present it in the most useful form, " he says.

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