¹⁵N-CPMAS nuclear magnetic resonace spectroscopy and biological stability of soil organic nitrogen in whole soil and particle-size fractions

Abstract

Soil organic nitrogen was quantified by solid-state ¹⁵N cross-polarization nuclear magnetic resonance spectroscopy (NMR) during a 14-month laboratory incubation of a sandy loam soil amended with ¹⁵N-clover. In whole soil and particle-size fractions, the clover-derived N was always 85-90% amide, 5 10% guanidinium N of arginine, and 5% amino. Quantitativeness of these results was suggested by (1) analysis of a standard containing a complex mixture of organic ¹⁵N and (2) correlation of spectral intensities with 15N concentrations. Based on the unchanging proteinaceous NMR signature of clover-derived N throughout the incubation, differences in the mineralization/immobilization kinetics of clover-N among the different particle-size fractions appeared not to be linked to organic functional group. Kinetic analysis of the mineralization of ¹⁵N, with correction of rate constants for field temperatures, suggested that the proteinanceous ¹⁵N in the clay and fine silt fractions observed here had a mean residence time of 7 years in the field.

Citation

DiCosty, R.J.; Weliky, D.P.; Anderson, S.J.; Paul, E.A. 2003. ¹⁵N-CPMAS nuclear magnetic resonace spectroscopy and biological stability of soil organic nitrogen in whole soil and particle-size fractions. Organic Geochemistry 34 (2003) 1635-1650