Remote Sensing Techniques for Nitrogen Stable Isotope Detection in Plant Matter

Research was conducted to develop the foundations of a new method, infrared nitrogen stable isotope (INSI) ratio, for calculating nitrogen stable isotope ratios using infrared data in plant matter. Laboratory plant growth experiments, using buckwheat and 15nitrogen enrichment, showed diagnostic wavelength shifts in the infrared. Data was collected at multiple frequencies that are associated with nitrogen functional group compounds. Computational modelling of common plant nitrogen compounds validate the spectral shifts and was used to identify ammonium as a unique compound for spectral data based ratio development. Field data was collected at locations using organic fertilizer, inorganic fertilizer and along known nitrogen impaired waterways in the Shenandoah Valley of the Chesapeake Bay watershed. The calculated INSI ratio values showed values consistent with expected levels of enrichment. The INSI ratio method developed in this research establishes the foundation for researchers to continue development of this new approach. In the future, infrared field based sensors could be developed that are tuned to the frequencies of 15N wavelength shifts identified in this research. This will provide researchers with faster and cheaper isotope ratio measurements covering broader areas and eventually be translated for use with airborne or space-based instruments.