To test this hypothesis, we established field trials of soybeans (Glycine max cv. Bravor) inoculated with either sterile culture solution (control) or isogenic strains of Bradyhizobium japonicum JH (Hup+, wild-type), JH47 (Hup- mutant) or 532C, and a non-inoculating Evans cultivar on a virgin field in Ottawa (Agriculture and Agri-Food Canada, Eastern Cereal & Oilseed Res Ctr,) that had not seen legumes for at least 20 years. We measured soil atmosphere N2O concentrations in the field, and soil N2O emissions in the laboratory using soils collected from soybean field. Soil adjacent to nodules had significantly higher rates of N2O production than soil near roots lacking nodules, a result consistent with the hypothesis and with previous studies using H2 treated soil, giving evidence of enhanced N2O emissions related to the legume symbiosis. In the field, variation of N2O emission over sample period was found in both soil static gas chamber and tube measurements. However, integrated over the sampling season, the soybean field inoculated with Rhizobia showed higher N2O emissions relative to non-inoculated field. In conclusion, our results give a possible explanation of why legume crops are often reported to have N2O emission rates that are higher than can be explained by N addition.