Molecular structure and bioavailability of soil organic N in prairie agricultural and wetland soils

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Organic nitrogen (N) compounds in the soil serve as both a source and sink for inorganic N and thus are important to the global N cycle. Soil organic N (SON) is decomposed by microorganisms, thereby releasing inorganic N (ammonium and nitrate) which is essential for agricultural production, but also can cause serious environmental pollution (e.g., nitrate contamination of groundwater and emissions of nitrous oxide, an important greenhouse gas). Despite the importance of SON, its chemical structure remains poorly understood. Indeed, one-third to one-half of SON typically is classified as 'unknown N' largely because research has been hampered by the absence of definitive analytical methods. Some advances were achieved by the application of modern analytical techniques such as pyrolysis-mass spectrometry and 15N nuclear magnetic resonance (15N NMR) spectroscopy but both techniques have been criticized due to analytical short-comings. Recently, the installation of Canada's first synchrotron facility, namely the Canadian Light Source (CLS) at the University of Saskatchewan, promises to provide Canadian researchers with the unique opportunity to use synchrotron-based techniques to examine soil organic matter and unambiguously document the nature of previously unidentified SON. The long-term objective of the proposed research is to characterize SON compounds using synchrotron-based techniques, with the ultimate goal of using this knowledge to predict soil N bioavailability (i.e., potential contribution to plant productivity and environmental losses), and identify and/or develop more user-friendly chemical soil tests to accurately estimate bioavailable N pools. By documenting SON structures at the molecular level, our ability to predict release of N into biologically and environmentally sensitive inorganic N pools will be greatly improved. This information is important to Canadian farmers who need to make informed decisions regarding efficient use of N fertilizers for agronomically and environmentally sustainable agriculture, and to other scientists who strive to model environmental N losses, including greenhouse gas emissions.