Monday, November 5, 2007
96-7

Nitrous Oxide Production in an Eastern Cornbelt Soil: Sources and Redox Range.

Guillermo Hernandez-Ramirez1, Sylvie M. Brouder1, Douglas Smith2, George E. Van Scoyoc1, Timothy Filley3, and Greg Michalski3. (1) Purdue University, Lilly Hall of Life Sciences, 915 W. State Street, West Lafayette, IN 47907-2054, (2) USDA-ARS National Soil Erosion Research Lab, USDA-ARS National Soil Erosion Research Lab, 275 S. Russell Street, West Lafayette, IN 47907-2077, (3) Dept. of Earth and Atmospheric Science, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47900

Nitrous oxide derived from soils is a main contributor to the greenhouse gas effect and ozone layer depletion; however, sources and regulation are not clearly understood. This study was conducted to estimate magnitude and sources of nitrous oxide (N2O) production as affect by N source, soil water content and redox potential. Soils sampled from continuous corn experimental plots after receiving eight consecutive years of either side-dressed urea-ammonium nitrate (UAN) or fall liquid swine manure (FM) were aerobically and anaerobically incubated. Soil N2O sources were traced by 15N-labeling. Partitioning results were highly variable but suggested enhanced denitrification after an extreme increase in soil water content (from 45 to 90 % WFPS), and a more coupled nitrification – denitrification at moderate water content (55 % WFPS). Manured soils at high water content registered higher (102 vs. 15.3 μg N2O kg-1 soil), shorter-lived (4 vs. 7 days) N2O production than at moderate water content. Comparing N sources in anoxic conditions, manured soils showed higher N2O production rates than UAN (up to 336 and 145 μg N2O kg-1 soil h-1, respectively) shortly after flooding (day 1 to 4) coinciding with a sharp drop in redox potential (575 to 466 mV). Redox potential range for N2O production occurred at moderate reducing conditions (420 to 575 mV) and was not affected by N source. Soils were consistent net N2O producers as function of water regime and N input, particularly when receiving annual fall manure applications.

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