Atmospheric N fixation contributes 65% of the N for terrestrial ecosystems with two type of legumes based on the form of N exported to the plant. One type of legume, which includes alfalfa, transports fixed N as the amino acid glutamine and the second type of legumes, which includes soybean, transports compounds called ureides. What little is known about the ureides, allantoin (AT) or allantoic acid (AA) is their structure. At present, a non-selective colorimetric detection method is the only published method coupled with a hot water extraction. An improved ion chromatographic (IC) separation with pulsed amperometric detection method was tested, which identified the ureides and all amino acids and found that the hot water extraction rapidly degraded the AA present to urea. Improvement to the extraction methods from ureide-spiked soils found cold water or cold 0.2 M NaOH was also effective for ureide extraction while limiting degradation. Extraction of the two types N fixing plants found all contained AA and urea but AT was not detected. Incubations (20 g soil, 100 mg N kg^-1soil; 250 mL Erlenmeyer) with Midwest and an Arizona rangeland soils exposed to desert legume species found very rapid similar release of C with addition of the AA and urea and a slower mineralization of AT. The Midwest soil and the Arizona soil produced similar amounts of mineralized C, but the Midwest soil produce 6 to 14 times the nitrous oxide from the AA, AT and urea additions and the rate of nitrous production in the Midwest soil was rapidly increasing at the end of the two week incubation. Nitrate production from the N additions during the Midwest soil incubation was nearly 10 times the rate compared with the Arizona soil.