An acid dichromate digestion procedure for total nitrogen determination in soils

Abstract

Modified version of a dichromate digestion procedure, earlier found suitable for simultaneous determination of organic carbon (C) and potentially mineralizable nitrogen (N) in soils, was evaluated for total N determination in 44 diverse soil samples from the semi‐arid region of India. The soils belonged to Vertisols and Alfisols and had a wide range in total N contents. The method involves digestion of the soil sample with an acidified dichromate solution for 30 minutes in a digestion tube in a block digester preheated to 165°C followed by determination of N in the digest by steam distillation procedure. The efficacy of the dichromate procedure for determining total N differed for the two soil types. Excellent correlations were observed between the values of total N obtained by the dichromate procedure (Dichro‐N) and by Kjeldahl method (Kjeldahl‐N) for Vertisols (R²=0.995; n=21) and Alfisols (R²=0.952; n=23). The regression equations describing the relationships between the two soil types can be used to estimate Kjeldahl‐N from Dichro‐N. Both Kjeldahl and the proposed acid dichromate methods were found to be more precise in determining total N in Vertisols than Alfisols. The proposed procedure is rapid and simple and can be used for routine total N determination especially, in soils such as Vertisols. Based on our results the acid digestion procedure certainly deserves a wider evaluation with a range of soil types.