Amino Acid15N/14N Analysis at Natural Abundances: A New Tool for Soil Organic Matter Studies in Agricultural Systems

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Abstract
The effects of landuse, fertilizer history and soil type on the quantity and isotopic quality of hydrolysable soil amino acids were examined in 3 grassland and 2 arable soils. Results showed, (i) that overall concentrations of individual amino acids were highest in the grassland soils, (ii) that ‰δ15N values of the individual amino acids differed considerably between the five soils, and (iii) that the combination of amino acid ‰δ15N values and concentrations could be used to distinguish between landuse, crop type and fertilizer history. This preliminary study indicates that the pathways of transformation of soil amino acid N are influenced by long term N inputs and that associated biological processes are reflected in differences in concentrations and ‰δ15N values of individual soil amino acids.