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 Comments on Ken Ferrie’s Corn/Soy Expo Nitrogen Management Presentation Minimize
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Posted by: WCM Staff 2/13/2008 3:55 PM
Commenbs on an interesting presentation by Mr. Ken Ferrie on nitrogen management. The Corn/Soy Expo presentation covered a number of issues and suggested several practices that are not part of Wisconsin’s nitrogen management recommendations.

Comments on Ken Ferrie’s Corn/Soy Expo Nitrogen Management Presentation

 Larry Bundy, Professor Emeritus, and Richard Wolkowski, Extension Soil Scientist, Department of Soil Science

Recently, we attended the Wisconsin Corn/Soy Expo and had the opportunity to hear an interesting presentation by Mr. Ken Ferrie on nitrogen management. The presentation covered a number of issues and suggested several practices that are not part of Wisconsin’s nitrogen management recommendations. The comments below are intended to connect several points in Mr. Ferrie’s presentation to current Wisconsin nitrogen (N) management guidelines.

Mr. Ferrie spent some time discussing the amounts of N that could be tied up or immobilized during the decomposition of corn and soybean residues. Growers should know that the current Maximum Return to Nitrogen (MRTN) nitrogen rate guidelines for corn following corn or corn following soybean were developed from numerous field N response experiments conducted in the presence of those crop residues. Therefore, any effect of the residue on the amount of N needed to achieve optimum yields is included in the MRTN rate suggestion. 

(See http://www.soils.wisc.edu/extension/hottopics/NGuidelinesNPM.pdf ) and  ( http://www.soils.wisc.edu/extension/hottopics/N-to-corn-ratios-07.pdf  )

The current guidelines also suggest that the high end of the MRTN rate range be used if corn residue cover is greater than 50%.   It is not necessary or desirable to make further adjustments to these N rates to account for residue effects. Most states in the region, including Iowa, Minnesota, and Wisconsin are using the MRTN approach for their corn N rate guidelines.

Immobilization of N by crop residues was discussed as an isolated issue instead of as a component of the simultaneous immobilization and mineralization reactions that occur in soils during the growing season. The net effect of these simultaneous reactions is the release of plant available N because mineralization of N from organic matter is much greater than the amount of N tied up in residues. This is why a yield response is not likely if “extra” fertilizer N is added to offset N immobilized by residues. The absence of yield response to N applied to assist in decomposing residues was documented in the following research.
 
A three-year Wisconsin study measured the effects of fertilizer N applied to corn residue in the fall on no-till corn yields and N response the following year.   Results showed no effect of N applied to the residue on yields or the rate of residue decomposition. See
 
Finally, the Illinois Soil Nitrogen Test (ISNT) was suggested in Mr. Ferrie’s presentation as a method of identifying fields that would not respond to N fertilization or had low optimum N rate requirements. The ISNT has been thoroughly evaluated in university research in the North Central Region and has generally shown no ability to identify N responsive fields or optimum N rates for corn. In Wisconsin, where the test was evaluated in 80 corn N response experiments, the ISNT could not identify N responsive sites, could not separate first-year corn after alfalfa from continuous corn, and was not useful for identifying optimum N rates for corn. The ISNT value can be accurately calculated from a routine soil organic matter test, but that value is no more useful for predicting crop N needs than the organic matter measurement. 
 
The recommendation for corn N management in Wisconsin is supported by research that shows that rate should be based on the MTRN approach accounting for the yield potential of the soil and the previous crop. Apply N fertilizers using methods and timing that limit loss through volatilization, leaching, and denitrification. Take credits for forage legumes, manure, and other organic waste materials when appropriate. Soil nitrate tests such as the pre-plant nitrate test and the pre-sidedress nitrate test can be used to fine-tune N rate.
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