Evaluation of a rapid chromic acid method for determination of total nitrogen in soils

Abstract

Abstract A chromic acid method proposed for rapid determination of total nitrogen (N) in soils was evaluated by comparing its results with those obtained by a Kjeldahl method commonly used for total N analysis of soils. Analyses of 12 surface soils selected so that they differed markedly in texture and organic carbon content showed that the chromic acid method recovered only 87.5% to 94.1% (average, 90.5%) of the soil N recovered by the Kjeldahl method. The recovery of N from ammonium sulfate and soils by the chromic acid method decreased with increase in time of digestion with chromic acid from 1 minute to 15 minutes (the recommended digestion time). This indicates that the low recovery of soil N by the chromic acid method was at least partly due to oxidation of ammonium to nitrate and/or nitrite by chromic acid and subsequent gaseous loss of these forms of N. Support for this conclusion was provided by analyses showing that about half of the N that could not be recovered as ammonium after digestion of ammonium sulfate with chromic acid for 15 minutes was in the form of nitrate.