Location: Soil, Water & Air Resources Research2011 Annual Report
1a. Objectives (from AD-416)
(1) Compare the capabilities of leading analyses for nitrogen and carbon chemistry to identify and measure strongly bound aromatic forms of nitrogen in previously studied soil and humic samples from paddy fields where a nitrogen deficiency in rice crops was attributed to decreased availability of soil organic nitrogen. One method to be included in this comparative study is the newly developed K-edge x-ray absorption near edge structure spectroscopy (XANES), which is available at the Canadian Light Source, Inc. facility in Saskatoon, Saskatchewan, Canada. (2) Determine whether strongly bound aromatic forms of nitrogen have accumulated in poorly drained cropland soils of Canada and the Upper Midwest, U.S. that are under zero tillage, and determine whether their stabilization might have contributed to reports of nitrogen deficiency in these soils.
1b. Approach (from AD-416)
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.
3. Progress Report
ARS researchers mailed two sets of organic matter fractions to Canadian collaborators, who analyzed them at the Canadian Light Source facility by K-Edge X-Ray Absorption Near-Edge Structure spectroscopy for chemical forms of nitrogen molecules. Project monitoring is maintained among ARS researchers and collaborators through email correspondence and occasional telephone conversations.