An acid dichromate digestion procedure for total nitrogen determination in soils
2000
Sahrawat, K.L. | Murthy, K.V.S.
Modified version of a dichromate digestion procedure, earlier found suitable for simultaneous determination of organic carbon 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 digest preheated to 165 degrees 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 soil types.
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