Amino acid N-15/N-14 analysis at natural abundances: A new tool for soil organic matter studies in agricultural systems

The effects of landuse, fertilizer history and soil type on the quantity an d isotopic quality of hydrolysable soil amino acids were examined in 3 gras sland and 2 arable soils. Results showed, (i) that overall concentrations o f individual amino acids were highest in the grassland soils, (ii) that par ts per thousand delta(15)N values of the individual amino acids differed co nsiderably between the five soils, and (iii) that the combination of amino acid parts per thousand delta(15)N values and concentrations could be used to distinguish between landuse, crop type and fertilizer history. This prel iminary study indicates that the pathways of transformation of soil amino a cid N are influenced by long term N inputs and that associated biological p rocesses are reflected in differences in concentrations and parts per thous and delta(15)N values of individual soil amino acids.