Further Evidence for the Inability of the Kjeldahl Total Nitrogen Method to Fully Measure Indigenous Fixed Ammonium Nitrogen in Subsoils

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Abstract
Three methods of Kjeldahl total N determinations in soils were compared. Method 1 involved a pretreatment of the soil with a HF‐acid mixture and resulted in higher N values than methods 2 or 3 which involved a long period of digestion and a modification of a Gunning method, respectively. Differences in total N values obtained by the three methods were greatest for subsoils. The inability of methods 2 and 3 to measure all of the indigenous fixed NH4+‐N resulted in low N values and erroneously high C:N ratios in the subsoil.
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