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Nitrous Oxide Emissions from Irrigated Sorghum
Welzmiller, J.T., Matthias, A.D., White, S. and Thompson, T.L. 2008. Elevated carbon dioxide and irrigation effects on soil nitrogen gas exchange in irrigated sorghum. Soil Science Society of America, Journal 72: 393-401.

The authors write that "increased atmospheric CO2 may change nitrogen cycling in soils," while noting more specifically in this regard that "nitrous oxide [N2O] is of growing concern because of its relatively long atmospheric residence time (114-120 years)" and because it is about "300 times more radiatively active than CO2."

What was done
Because of these concerns, Welzmiller et al. measured N2O and denitrification emission rates in a C4 sorghum [Sorghum bicolor (L.) Moench] production system with ample and limited flood irrigation rates under Free-Air CO2 Enrichment (seasonal mean = 579 ppm) and control (seasonal mean = 396 ppm) CO2 during the 1998 and 1999 summer growing seasons at the experimental FACE site near Maricopa, Arizona (USA).

What was learned
When all was said and done, the four researchers found that "elevated CO2 did not result in increased N2O or N-gas emissions with either ample or limited irrigation," which findings they describe as being "consistent with findings for unirrigated western U.S. ecosystems reported by Billings et al. (2002) for Mojave Desert soils and by Mosier et al. (2002) for Colorado shortgrass steppe."

What it means
In discussing the implications of their findings, Welzmiller et al. say their results suggest that "as CO2 concentrations increase, there will not be major increases in denitrification in C4 cropping environments such as irrigated sorghum in the desert southwestern United States," which further suggests there will not be an increased impetus for global warming due to this phenomenon.

Billings, S.A., Schaeffer, S.M. and Evans, R.D. 2002. Trace N gas losses and mineralization in Mojave Desert soils exposed to elevated CO2. Soil Biology and Biochemistry 34: 1777-1784.

Mosier, A.R., Morgan, J.A., King, J.Y., LeCain, D. and Milchunas, D.G. 2002. Soil-atmosphere exchange of CH4, CO2, NOX, and N2O in the Colorado shortgrass steppe under elevated CO2. Plant and Soil 240: 201-211.

Reviewed 4 June 2008