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Studies look at corn nitrogen requirements

By Jean Caspers-Simmet

Date Modified: 07/15/2013 9:57 AM

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NASHUA — Extension soil fertility specialist John Sawyer shared results from two nitrogen studies at last week's field day at the Northeast Research Farm at Nashua.

One study looks at seasonal and rotational influences on corn nitrogen requirements. The other looks at corn nitrogen fertilization requirements and corn/soybean yield response when grown in a rye cover cropping system.

The first study researches nitrogen fertilization needs in continuous corn and corn rotated with soybeans. Multiple rates of nitrogen were spring applied with yield response to nitrogen within each rotation measured on a yearly basis for multiple years at multiple sites.

Corn yields were good for both corn rotated with soybeans and continuous corn despite 2012's dry growing season, Sawyer said.

The calculated economic optimum nitrogen rate in 2012 was opposite of normal for corn rotated with soybeans at 148 pounds N/acre compared with 120 pounds N/acre for continuous corn.

The corn yield at the EONR was 28 bushels per acre higher in the corn rotated with soybean rotation compared to continuous corn.

"For the past eight years, corn yield has averaged 12 percent higher in the corn rotated with soybeans, 201 versus 177 bushels per acre," Sawyer said. "Soybean yield in the corn rotated with soybeans averaged 63 bushels per acre in 2012."

Despite the large variation in yield between the years, the economic optimum nitrogen rate and the maximum return to nitrogen rate resulted in corn yields quite close to the maximum.

"These results indicate that the maximum return to nitrogen rate does provide for optimal economic corn grain production, and like EONR, yields close to the maximum yields each year," Sawyer said.

With the rye cover crop study, Sawyer applied multiple rates of nitrogen fertilizer, with measurement of corn yield response to applied nitrogen and soybean yield with and without a fall planted winter rye cover crop.

For 2012 the winter rye cover crop was no-till drilled at 1 bushel per acre in fall 2011 after soybean and corn harvest. The rye cover crop growth was controlled with Roundup in the spring with targeted control at least 14 days before corn planting and one week before soybean planting. Corn and soybean crops were no-till planted in 30-inch rows in April for corn and May 11 to 17 for soybeans. Nitrogen fertilizer rates were applied sidedress within two weeks after planting as urea ammonium nitrate solution at 0, 40, 80, 120, 160 and 200 pounds of nitrogen per acre.

Rye growth and above ground biomass production have varied between years and sites due to differences in spring conditions and the prior-year crop, Sawyer said. In 2012, rye biomass dry matter was greatest before soybean planting. Rye biomass also was greater with increasing prior-year nitrogen rate applied to corn. As in past years, soybean grain yield was not affected by the rye cover crop. Yield was the same.

Across sites in 2012, corn yield at the maximum nitrogen response rate was three bushels per acre lower when planted in conjunction with the rye cover crop, Sawyer said. However, yield was greater with rye at Crawfordsville but lower at all other sites with rye. Corn grain yield has been lower each year with the rye cover crop, 5, 20 and 7 bushels per acre in 2011, 2010 and 2009 respectively.

"Across the four years of study, there was an average 10 lb. nitrogen per acre higher economic optimum nitrogen rate and a 5 percent lower corn yield with the rye cover crop," Sawyer said.