Carbon and nitrogen analysis of soils by automated combustion techniques

Abstract

Studies with 20 soils containing from 7 to 204 g kg^‐1 total carbon and from 0.5 to 16.9 g kg^‐1 total nitrogen indicated that the Leco CR‐12 Carbon Determinator and the Leco CHN‐600 Elemental Analyzer are satisfactory for routine analysis of soils for total carbon and that the Leco CHN‐600 Elemental Analyzer is also satisfactory for routine analysis of soils for total nitrogen. The two Leco instruments evaluated are automated analyzers in which the sample under analysis is combusted by heating it to a high temperature by a resistance furnace in a stream of purified oxygen. In both instruments, the CO₂ produced by combustion is measured by a selective, solid state, infrared detector. In the Leco CHN‐600 instrument, the N₂ produced by combustion is measured by a thermal conductivity cell. With all 20 soils analyzed, the results of total carbon analysis by the Leco CR‐12 and CHN‐600 instruments agreed closely with those obtained by the wet‐combustion method of Allison, and the results of total nitrogen analysis by the Leco CHN‐600 instrument agreed closely with those obtained by the Kjeldahl method commonly used for soil analysis. The two Leco methods evaluated are rapid and precise, and they seem well suited for routine analysis of soils.