Dry Nitrogen Products for Fall and Spring Application in Northern Illinois.

Fall applied nitrogen (N) continues to be a popular fertilization practice in the Corn Belt.  Urea is not recommended for fall or winter applications as large potential losses of N can occur, but it is becoming a more common source.  New urea containing materials have been developed as a means to minimize N losses but little is known about their behavior with fall applications.  The objective of this research was to evaluate the effect of N sources on the success of fall applied N for corn production and compare it with the spring application of these materials.  The project was conducted at DeKalb for three growing seasons to study the effect of N application time (fall and spring), N materials (ammonium sulfate, urea, SuperU and ESN), and N rate (0-200 kg N/ha) on corn grain yield and N concentration.  On average, grain yield for spring (15.5 Mg/ha) N application was significantly (p<0.05) higher than fall application (14.9 Mg/ha).  Maximum yield for spring application was achieved with 166 Kg N/ha whereas fall applied N required 210 kg N/ha.  SuperU resulted in higher corn yields than ESN when applied in the fall, but not in the spring. Neither of these materials resulted in significantly higher corn yields than urea alone at either application time. Grain protein concentration was significantly higher for spring applied than fall applied N and this difference was larger as N rate increased. There was no source effect on grain protein concentration. This three year study suggests that urea could be applied in the late fall in Northern Illinois.