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Molecular scale investigations of the interaction of soil organic N with soil minerals

EMSL Project ID


The association of organic nitrogen (N) compounds with soil minerals is an important mechanism for determining the long-term persistence of N in soils and N bioavailability. Mounting evidence points out that N-rich residues preferentially attach to mineral surfaces. In fact, more than 70% of total soil organic N (SON) is associated with mineral surfaces as mineral associated organic N (MAON). However, the mechanisms of preferential adsorption of SON onto minerals are still not clear. One of the most abundant forms of SON is N-containing monomeric amino acids (AA), which contribute 30-45% of SON. A previous batch experiment and FTIR spectra have shown that the adsorption of amino acids onto clay surfaces relies on the amino group. In contrast, another study using ATR-FTIR methods highlights the importance of carboxylate groups in the sorption process of amino acids. The contradictory interpretations found in the literature likely reflect the difficulty involved in interpreting subtle FTIR spectral changes. The specific adsorption of different C compounds is closely related to minerals’ active adsorption sites. In fact, only less than 19% of mineral surfaces were found to show ON attachment. Whether amino acids are absorbed on the surface or edge site of minerals through carboxyl groups or amine groups as well as the direct bonding strength of various amino acids with different minerals are unknown at molecular scale. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been proven to be a powerful analytical tool in providing elemental and molecular information as well as the adsorption site of organic C with minerals. In addition, atomic force microscopy (AFM) combined with dynamic force spectroscopy (DFS) recently have been shown to be a powerful technique to measure the direct bonding strength between a single functional group and a mineral surface. This project aims to increase our understanding of the direct bonding mechanisms and active adsorption sites of organic N (amino acids) with different soil minerals and thus enhance our understanding of the controls on bioavailability of soil N. We propose to use a novel combination of cutting-edge methods available at EMSL (ToF-SIMS, NanoSIMS, and AFM-DFS) to directly characterize the binding mechanisms and strengths of amino acids absorbed to mineral surfaces. Combined with macro scale batch experiments done on our campus, these results will give us a mechanistic and better predictive understanding of the interactions of soil organic N compounds with minerals, which will have important implications for managing SON and nutrients in agricultural ecosystems.

Project Details

Project type
Large-Scale EMSL Research
Start Date
End Date


Principal Investigator

Yuan Liu
Michigan State University


Lisa Tiemann
Michigan State University