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

item Hernandez Ramirez, Guillermo
item Smith, Douglas

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2008
Publication Date: 5/13/2009
Citation: Hernandez Ramirez, G., Brouder, S.M., Smith, D.R., Van Scoyoc, G.E., Michalski, G. 2009. Nitrous Oxide Production in an Eastern Corn Belt Soil: Sources and Redox Range. Soil Science Society of America Journal. 73:1182-1191.

Interpretive Summary: Nitrous oxide is a very important greenhouse gas, and agricultural soils can emit relatively large amounts of this gas. Increasing concentrations in the atmosphere of nitrous oxide are known as responsible for global warming effect. In this study, soil samples were collected from corn fields in Indiana. These soil samples were incubated in closed jars and bottles under different conditions, and concentrations of nitrous oxide were measured at least five times during one to two weeks. In general, we observed that nitrous oxide emissions were not different among corn fields fertilized with chemical nitrogen versus liquid swine manure. Also, nitrous oxide production was higher with greater soil water content as expected. In addition, the combination of liquid swine manure with high water content resulted in the highest nitrous oxide production in this experiment. This research suggests that soils receiving manure additions are more likely to produce more nitrous oxide particularly when these soils are subject to extreme rewetting events. This research is important to growers, scientists, and policy-makers interested in nitrogen management practices that can reduce the contribution of agricultural soils to global warming effect.

Technical Abstract: Nitrous oxide (N2O) 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 magnitude and source (nitrification vs. denitrification) of N2O production as affected by form of nitrogen (N) fertilizer, soil water content, and redox potential (Eh). Soils from continuous corn experimental plots with a history of eight consecutive years of either side-dressed urea-ammonium nitrate (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 enhanced denitrification occurred after an extreme increase in soil water content (from 45 to 90% 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). Comparing between N fertilizer sources in 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 (575 to 466 mV). Irrespective of the N sources, a narrow, consistent Eh range for N2O production occurred at moderate reducing conditions (420 to 575 mV). These results indicate that soils, receiving repeated manure application, that are subject to intensive, recurrent soil re-wetting events may be prone to higher N2O emission.