New corn nitrogen rate recommendations


ST. PAUL, Minn. — With substantial increases in the prices of fertilizer nitrogen (N), farmers are encouraged to re-evaluate their N rates for corn for the greatest economic return on their N investment.

A handy, simple and convenient tool to help growers arrive at the optimum economic N rate is the Corn N Rate Calculator found on the Iowa State University Web site at

Three factors

The calculator considers three factors: the price of fertilizer N, the anticipated corn price (both established by the user) and the database containing corn yield response to N developed by university scientists in Illinois, Iowa, Minnesota and Wisconsin.

Armed with yield response data from almost 700 corn belt sites, this new approach was found to be far superior to the old approach used by many, according to Gyles Randall, soil scientist with the University of Minnesota.

That involved multiplying yield goal in bushels per acre times some constant (such as 1.2 or 1.0 pound N/bushel) to arrive at a recommended N rate.

Using this new approach and the calculator, farmers have an N rate that maximizes economic returns to N and the profitable N rate range that will give an economic return within $1 per acre of the maximum return.

Moreover, farmers can input various fertilizer N and corn price combinations to see how these factors affect optimum economic fertilizer N rate.

Database updated

The database for the calculator was recently updated with new N rate information from 31 field research sites in Minnesota.

The calculator now contains yield data from replicated studies at 128 sites in 25 Minnesota counties from 1990 through 2007.

Fifty-eight percent of the sites were on farmers’ fields, ranging from the Iowa border on the south to Ottertail county on the north, and from Winona County to the South Dakota border.

Corn yields at these sites ranged from 130 to 243 bushels per acre, with average yields of 167 and 176 bushels per acre when following corn and soybeans, respectively.

In this era of fluctuating high prices, farmers using N rates provided by the calculator coupled with other best management practices for nitrogen will be able to obtain the greatest economic return on their fertilizer N investment.


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