Field soils near Beltsville, MD, and Texcoco, Mexico were sampled, pressed into disks, air dried, and analyzed by laser-induced breakdown spectroscopy (LIBS) in the field at each site. LIBS spectra were collected using a Spectrolaser 1000HR, and the LIBS spectra were converted to carbon concentrations. Calibration curves were developed from soils collected throughout the Midwest U. S. and did not include the test sites in Maryland or Mexico. Thus, these calibration data were independent of soil texture and were not related to the fields where testing occurred. Carbon concentrations from LIBS analyses using the “universal” calibration compared favorably with dry combustion data collected from the Maryland and Mexico test sites. Also, a separate calibration curve developed from dry combustion samples and LIBS samples only from the test site compared favorably with the other carbon concentrations. Overall, LIBS analysis and use of previously developed calibration curves is rapidly becoming an analytical method capable of high accuracy and precision in the field.