Using anion chromatography–pulsed amperometry to measure amino compounds in dairy manure-amended soils
Amino acids and amino sugars comprise the bulk of soil N, so information on their chemical forms and cycling patterns should enable better understanding of soil N cycling. In this study of soil samples that had received animal manure, we evaluated the capabilities of a recently developed analysis for soil amino compounds (19 amino acids, two amino sugars) that consists of methanesulfonic acid extraction, anion chromatography, and pulsed amperometry detection. Soil samples were taken from a 28-d laboratory incubation of nine soils from six soil orders in six U.S. states that were amended with dairy manure slurry at a rate to simulate 300 kg N ha–1. Manuring resulted in enrichment of the soils by nearly all measured amino compounds but to varying degrees. These enriched levels were relatively stable against mineralization during the short-term incubation, with most compounds having decreased modestly in concentration (mean 11%) by the end of the incubation, in contrast to slight increases (mean 3%) for three compounds that are associated with microbial activity and were not overly abundant in the manure: ornithine, glucosamine, and galactosamine. Several measurements of the extracted amino compounds varied significantly among the nine soils. Our results illustrated some shortcomings of this analytical approach, including instability of small peaks and the need for a second extraction mode to maximize extraction of certain amino compounds. We identified 41 to 43% of the total soil N as amino compounds for all soils and treatments, which is comparable to results reported previously for the conventional analysis involving HCl extraction and cation chromatography. Compared with conventional analysis, this approach might more efficiently extract basic amino acids and less efficiently extract acidic amino acids. Overall we found this approach to be a useful analysis.