Effect of Nitrogen Fertilizer Application on Corn Residue Decomposition in Iowa

Abstract

Core Ideas Application of 32% urea ammonium nitrate after harvest has no effect on residue decomposition. Three months after N addition, 54 to 69% of residue remained with no N rate differences. The remaining amount of residue after 12 mo was 35 to 49% across all N treatments. Incubation study shows soil temperature as a major factor in residue decomposition. Nitrogen addition suppressed CO2–C evolution during residue incubation. Corn (Zea mays L.) residue is one of the sources of soil organic carbon (SOC) in row cropping systems in the Midwest. Farmers in Iowa apply liquid N to corn residue after harvest, assuming it will increase corn residue decomposition. The objective of this study was to investigate the effectiveness of N application for increasing corn residue decomposition. The study included two fields with three N rates (0, 34, or 67 kg N ha−1) of liquid 32% urea ammonium nitrate (UAN) applied after harvest, and two laboratory incubation experiments with three temperatures (0, 25, and 35°C) in 2012 and 2013. The experiment design was a randomized complete block in four replications in a no‐tillage system (NT). The average mass of residue organic carbon (OC) after harvest was in the range of 1.6 to 1.7 Mg ha−1. Residue OC in the field declined sharply in both years, particularly during the first 3 mo, with no significant difference between N treatments. The only difference in field residue decomposition occurred after 6 mo (P = 0.0241) at the Olson location in 2012, where a greater (>21%) amount of remaining OC was associated with 0 kg N ha−1 than with other N treatments. The incubation study showed an increasing rate of residue decomposition with increasing soil temperature with no N application effects on residue decomposition. These findings show that air and soil temperatures are the driving force for residue decomposition, especially at 25°C, rather than with N addition.