Automated instrumental analysis of carbon and nitrogen in plant and soil samples

Abstract

Abstract An automated CHN Analyzer was compared with the Walkley‐Black and Kjeldahl methods for organic carbon (C) and nitrogen (N). Four organic compounds, twenty nine plant materials and five soils were tested. The CHN Analyzer gave C and N values that were not significantly different (P<0.05) to the theoretical weight percents of the organic compounds. The Walkley Black method gave soil C values significantly lower (P<0.05) than those obtained with the CHN Analyzer. The Kjeldahl method gave soil N values significantly lower (P<0.05) than the CHN Analyzer on three of five soils tested. The discrepancies observed between methods appear to be due to different oxidation efficiencies. CHN Analyzer and Kjeldahl N analyses were not significantly different (P<0.05) for the plant materials except where samples contained greater than 0.7% NO3‐N. Potassium nitrate was also added as a spike to a tall fescue sample. Based on recovery of the spiked NO3‐N, the Kjeldahl method was a poor measure of total N for plant materials containing greater than 0.7% NO3‐N. The findings suggest the CHN Analyzer can be used for the rapid, accurate and simultaneous determination of C and N in plant and soil samples. Key words: Total nitrogennitrogen analysiscarbon analysiscombustion analysiselemental analyzerKjeldahlcrude protein Notes Paper number 87737 of the Idaho Agricultural Experiment Station Research Associate and Professor, respectively. Soil Science Division, College of Agriculture, University of Idaho, Moscow, Idaho, 83843.