2009 Year in Review

From the Fields

Nitrogen fertilizer and energy prices have prompted questions on the nitrogen replacement value of alfalfa when followed by corn. In other words, what is the first year nitrogen credit for field corn following alfalfa in northern Illinois?

Earlier research in Iowa, Wisconsin, Minnesota, and Pennsylvania involving 61 sites revealed a corn grain yield response to nitrogen fertilizer following alfalfa at seven of those sites. The optimum nitrogen rate at those seven locations ranged from 25 to 42 pounds per acre.

The Illinois Agronomy Handbook indicates that first year corn following an alfalfa stand of 5 plants or more per square foot, the nitrogen rate can be reduced 100 pounds per acre. If there are 2 to 4 plants per square foot, the nitrogen rate can be reduced 50 pounds per acre.

With improvements in corn hybrids and the increases in fertilizer cost and corn price, nitrogen rate studies for first year corn following alfalfa were conducted in 2007 and 2008 by University of Illinois Extension and funded by SARE (Sustainable Agriculture Research and Education). Sites were farms in Bureau and Stephenson counties and the University of Illinois Agronomy Research Center in DeKalb County.

At all locations, nitrogen rates of 0, 40, 80, 120, 160, and 200 pounds per acre were applied postemergence to corn.

Age of the alfalfa stand varied over the years and sites, but there were at least 4 plants per square foot. With a nitrogen price to corn price ratio of 0.15 (for example $0.60 per pound nitrogen and $4.00 per bushel corn) the optimum nitrogen rate was 48 pounds per acre. As the ratio increases or decrease, the optimum nitrogen rate also changes.

It is the intent to continue the studies in 2009. Further information is available by contacting Jim Morrison, Extension Crops Educator, 815-395-5710, or email morrison@illinois.edu

by Dawn Zuidema, theCity1.com
March 9, 2009