Start Date: Jan 01, 2011
End Date: Dec 31, 2015
To build on previous characterizations for the carbon and nitrogen chemistry of soil and humic samples from rice fields, we will analyze these same samples using a newly developed technique for nitrogen (N) and carbon chemistry, K-edge x-ray absorption near edge structure spectroscopy (XANES), which is available at the facility of the Canadian Light Source, Inc. a third-generation (i.e. most advanced) synchrotron at the University of Saskatchewan, Saskatoon, Canada. We will examine the previously identified N-bonded aromatic compounds in soils collected from Philippine rice fields that had experienced grain yield declines and were previously analyzed by advanced solid-state nuclear magnetic resonance (NMR) spectroscopy. We will compare these NMR findings of anilide N and heterocyclic N with N-XANES. Additionally, we will examine soils collected from long-term zero-tillage soils in Canada and the Upper Midwest of the U.S. that have reportedly experienced reduced N availability and yield declines, using N-XANES. The synchrotron studies will be coupled with more established techniques [i.e., amino acid analysis and NMR spectroscopy and pyrolysis field ionization mass spectrometry] to document the nature of previously unidentified soil organic N compounds using multiple techniques, and to elucidate mechanisms by which organic N is stabilized. We hypothesize that N-bonded aromatic compounds, such as those found in long-term rice production, similarly are present in long-term zero-tillage soils, and contribute to reduced N use efficiency and yield declines in these systems. Using multiple techniques to document and characterize soil organic N structures at the molecular level, this study aims to characterize the molecular composition and functions of key organic N pools, with the goal of identifying measureable bioavailable organic N pools and examining their implications for ecological functions within zero-tillage and conventional tillage agricultural ecosystems. This proposal will also enable a first-time comparison between all major analyses used for determining N forms in soil and humic samples. We will initiate our experiments using soils collected from rice-cropped fields that are known to have elevated levels of N-bonded aromatics. The N-XANES will be used to confirm the presence of these compounds. Our experiments then turn to examining soils that are likely to contain N-bonded aromatics (i.e., zero tillage soils). Thus, the unknown component of the research rests with the zero-till soils. If our experiments do not reveal N-bonded aromatics in the zero-till soils, we can refocus our experiments on the examination of soil N fractions from the rice-cropping soils.