Effect of Fall Nitrogen On Corn Residue Break Down in Illinois.

Challenges for continuous corn (Zea mays L.) production in no-till systems are often related to high volumes of crop residue that are thought to be more resistant to decomposition compared to earlier hybrids. An emerging practice in Illinois and other Midwestern states is to apply nitrogen (N) in the fall to help speed up residue decomposition. However, limited research has been done to determine the effectiveness of such practice. A two-year study at a research farm near Urbana, Illinois was established to investigate residue decomposition and stalk integrity of corn residue samples placed in mesh bags under no-till. The N treatments were liquid ammonium sulfate (21-0-0) and urea-ammonium nitrate (32-0-0) broadcast-applied in September, October and November at a rate of 34 kg ha^-1. Additional treatments of urea-ammonium nitrate at rates from 0 to 200 kg N ha^-1 were applied to determine corn grain yield response to N. Stalk strength was measured from September until April using a push penetrometer. Yields were limited by drought conditions during 2012, and the highest yield with the 200 kg N ha^-1 rate was only 7.2 Mg ha^-1. Across treatments, stalk strength decreased by 21% for the first year and 51% for the second year between late September and April 1 (when seedbed preparation normally begins). Residue from 2012 was weaker than 2011, possibly due to drought conditions. In 2012, by April 1, fall application of N, averaged across application time, reduced stalk strength by 12% relative to treatments receiving no N, but no decrease was observed by April 1, 2013. Treatments receiving N in September showed no differences in stalk strength relative to treatments receiving later N applications. No differences in stalk strength were observed between N sources. Preliminary results indicate that applying N in the fall to enhance decomposition is not warranted.