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The University of Minnesota Extension Service's nitrogen recommendations have been scrutinized the past couple of years by some crop consultants and fertilizer vendors who feel the N rates that are recommended for corn are not adequate.  A field trial was established in fall of 2000 at the Postdam research site to demonstrate the effect of N rates on corn.  This site was one of a series of several located in southern Minnesota.

Based on the "Nitrogen Fertilizer Task Force" recommendation, fertilizer N should not be applied in the fall on the loess soils overlying bedrock in southeast Minnesota.  However, for demonstration/research purposes a rate study was established with fall and spring N treatments.  Soybean was the previous crop.  The N source was urea (46-0-0) that was broadcast and incorporated (tandem disk) on 10' x 120' strip plots.  A check treatment was included and the plots were randomly arranged and replicated four times.  Corn was planted on May 1.  Weed control was excellent and there was little or no evidence of insect or disease incidence.  Yields were determined by hand harvest of random sections within each strip.

Based on this one year of data, the results are consistent with several years of research conducted on similar soil types in the region.  The optimum yield for corn that follows soybean can be achieved with N rates of 90 to 120 lbs N/A.  N rates that are applied at greater amounts are not cost effective and potentially cause excess nitrates to leach beyond the capacity of corn roots take up nitrate.  Therefore, the University of Minnesota recommendations look to be right in line where they should be for southeast Minnesota.