A method and device for taking non-invasive on-site soil carbon content and distribution measurements at the surface of the soil utilizing a neutron generator positioned on the surface of the soil to generate neutrons that penetrate the soil. The neutrons cause inelastic neutron scattering (INS) from carbon and subsequent emission of gamma rays from the first carbon excited level. The gamma rays are measured by a number of suitable on-site gamma ray detectors situated near the neutron generator. A nuclear spectroscopy system is utilized to generate an energy spectrum of the detected emitted gamma rays and a net number of gamma rays is determined by subtracting a background count from a total count at a predetermined energy level. The net count is then compared to a predetermined calibration plot to determine the weight percentage of carbon within the measured soil.