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SOIL BIOLOGY & BIOCHEMISTRY

Nitrous Oxide Production in an Eastern Corn Belt Soil: Sources and Redox Range

^a USDA-ARS, National Soil Tilth Lab., Ames, IA 50011-3120
^b Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907-2054
^c USDA-ARS, National Soil Erosion Research Lab., West Lafayette, IN 47907-2054
^d Dep. of Earth & Atmospheric Science, Purdue Univ., West Lafayette, IN 47907-2054

^* Corresponding author (Guillermo.Hernandez{at}ars.usda.gov).

Nitrous oxide derived from soils is a main contributor to the greenhouse gas effect and a precursor to ozone-depleting substrates; however, the source processes and interacting controls are not well established. This study was conducted to estimate the magnitude and source (nitrification vs. denitrification) of N₂O production as affected by the form of N fertilizer, soil water content, and redox potential (Eh). Soils from continuous corn (Zea mays L.) experimental plots with a history of eight consecutive years of either side-dressed urea–NH₄NO₃ (UAN) or fall liquid swine manure (FM) were collected and N₂O evolution was traced in both aerobic and anaerobic incubations using ¹⁵N labeling. Partitioning results were highly variable but suggested that enhanced denitrification occurred after an extreme increase in soil water content (from 45 to 90% water-filled pore space [WFPS]) while a more coupled nitrification–denitrification process drove N₂O evolution at moderate water content (55% WFPS). Manured soils at high water contents registered shorter duration peaks but with higher overall N₂O production rates than those observed at moderate water content (7-d weighted average of 0.61 vs. 0.09 µg N₂O kg^–1 soil h^–1). Under anoxic conditions, manured soils showed higher N₂O production rates than UAN soils (up to 336 and 145 µg N₂O kg^–1 soil h^–1, respectively) shortly after flooding, which coincided with a sharp drop in Eh (from 575 to 466 mV). Irrespective of the N source, a narrow, consistent Eh range for N₂O production occurred under moderate reducing conditions (420–575 mV). These results indicate that soils receiving repeated manure application that are subject to intensive, recurrent soil rewetting events may be prone to higher N₂O emissions.

Abbreviations: DOC, dissolved organic carbon • DW, distilled water • Eh, redox potential • FM, fall liquid swine manure • OVDE, oven-dried equivalent • PP, preplant • RM, repeated measures • UAN, urea–ammonium nitrate • WFPS, water-filled pore space