Chemical characterization and function of soil organic nitrogen in prairie agroecosystems

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My program focuses on soil N and N-cycling. Of particular interest has been the examination of soil organic N (SON) fractions with the goal of understanding how various organic N pools contribute to bioavailable N, both from an agricultural sustainability perspective (i.e., soil quality and soil fertility) and from an environmental perspective (i.e., environmental losses). The proposed research builds on existing work in which we use synchrotron-based N and C K-edge X-ray absorption near-edge structure (N- and C-XANES) to examine SON in bulk soil, and soil chemical and physical fractions. The long-term objective is to characterize the molecular composition of key chemical and physical SON pools, with the goal of identifying measureable bioavailable SON pools and examining their implications for ecological functions within agricultural ecosystems. The short-term objectives of the proposed research are: 1) to examine and characterize the occurrence and nature of unique SON compounds as affected by agricultural management practices and define relationships between the structure of these compounds and N bioavailability; and 2) to examine the speciation of SON in stable soil micro- and macro-aggregates, with the goal of elucidating potential mechanisms by which N (and C) is stabilized and protected in these physical fractions. Although others have used synchrotron radiation to examine soil and environmental samples, limited attention has been paid to SON largely due to the low levels of N typically present in soils, together with relatively low detection limits. Ongoing improvements to detections limits have opened new avenues for exploration of SON. Our work represents some of the earliest applications of N-XANES to soil and environmental samples, and we are well positioned to further advance this highly novel analytical technique as a defendable approach to examining SON at the molecular level, to resolve some of the controversy existing in the literature regarding the nature of SON, and to ascertain mechanisms by which SON is stabilized in soil chemical and physical (i.e., soil aggregates) fractions.