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Soil Amino Acid Composition Quantified by Acid Hydrolysis and Anion Chromatography−Pulsed Amperometry

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journal contribution
posted on 2003-10-22, 00:00 authored by Dean A. Martens, Kevin L. Loeffelmann
Soil organic N accounts for 95−98% of the total soil N content with amino acids (AAs) and amino sugars (ASs) identified as the major soil organic N compounds, but traditional 6 M HCl with reflux or sealed digestions for 24 h and various detection systems have accounted for only 30−40% of soil total N content as AA-N. This study compared traditional HCl extraction methodology with methanesulfonic acid (MSA) hydrolysis and nonderivatized AA and AS quantification by ion chromatography with pulsed amperometric detection for determination of the AA composition of plant litter and soils. MSA (4 M) gave AA-N recovery comparable to or better than 6 M HCl for plant AA digestions (16 h, 121 °C, 104 kPa). Use of 4 M MSA (0.5−1.5 h, 136 °C, 112 kPa) increased the total recovery of organic N as AAs, ASs, and NH4+ by 46% from soils (n = 22) compared with 6 M HCl (12 h, 110 °C, reflux) with a MSA recovery rate of 85.6% of the total N content (n = 22 soils). The shorter MSA soil digestions (0.5−1.5 h) suggested that the majority of soil organic N was not present as protein forms found in plant litter analysis (16 h of digestion). MSA ion chromatographic analysis for soil AA/AS composition is a robust nonderivatization method requiring little sample preparation that can distinguish between small changes in soil AA composition during one growing season due to vegetation and tillage managements. Keywords: Soil organic nitrogen; amperometric detection; soybeans; determination; analysis; corn; methanesulfonic acid; ion chromatography

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