Tuesday, November 14, 2006

Using Anion Chromatography-Pulsed Amperometry to Measure Amino Compounds in Animal Manure-Amended Soil.

Daniel C. Olk, USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011-4420, Ann-Marie Fortuna, USDA-ARS, New England Plant, Soil & Water Laboratory, Orono, ME 04469-5753, and C. W. Honeycutt, USDA-ARS, New England Plant, Soil & Water Laboratory, Orono, ME 04469-5753.

About 30-45% of total soil N can be identified as amino acids through the conventional sequence of soil extraction by HCl, separation of amino acids by ion exchange chromatography, ninhydrin derivatization, and detection by visible light absorption. Martens and colleagues identified 50% of total soil N as amino acids and amino sugars by using a slightly simpler procedure. Its steps were soil extraction by methanesulfonic acid during autoclaving, anion chromatography, and detection by pulsed amperometry. Derivatization is avoided. This procedure was used to study nine soils from six U.S. states that were amended with dairy manure at a rate of 300 kg N ha-1, including 130 kg organic N ha-1. Soils were incubated aerobically for 28 d under controlled conditions, with weekly sampling. The proportion of total soil N that was identified as individual amino compounds averaged about 50%, but this value was much greater (>70%) in two sandy, N-depleted soils than in most other soils. The effects of manure amendment on the suites of soil amino compounds were clear in the N-depleted soils but were not clear in finer textured, N-rich soils. Rates of N mineralization during the 28-day incubation varied among amino compounds. The rate of N mineralization for each amino compound also varied among soils, which may contribute to the observed large soil effect on manure-N mineralization. Given the inherent difficulty of distinguishing a single application of manure-N from a much larger background pool of soil organic N, results suggest that this analysis for amino compounds merits further application for elucidating soil N dynamics.

Handout (.ppt format, 486.0 kb)