A convenient semi‐micro procedure for total N analysis (including NO 2 ‐ and NO 3 ‐ ) of soil and plant material is described. The sample plus KMnO 4 , H 2 SO 4 , and Fe is initially placed in a test tube and heated in a water bath (90°C). Final digestion with concentrated H 2 SO 4 occurs in a heated Al (to 370°C) block. The NH 4 + content of the cooled tube contents is determined by steam distillation. This method allows simultaneous digestion of 60 samples, is inexpensive, accurate and precise, and includes NO 2 ‐ and NO 43 ‐ in the total N estimation.
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Douglas et al. (1980) studied this question.