Feigenbaum, S., Division of Soil Chemistry and Plant Nutrition, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Hadas, A., Division of Soil Chemistry and Plant Nutrition, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel

The low nitrogen concentration in soil extracts relative to other salts in the extracting solution and the high nitrogen concentration in a small volume required for analysis by emission spectrometry require the separation of nitrogen from other salts of the extract and its concentration. Nitrogen was separated from the extracts by reduction to ammonium and distillation. In comparing boric acid and sulfuric acid as ammonium acceptors, boric acid was proved to be unsuitable because unsatisfactory samples for15N analysis were obtained and the probability of failure in sample preparation was high. Two methods of concentrating the ammonium were compared: 1) Evaporation to dryness after steam distillation and redissolving the ammonium salt in a small volume; 2) Microdiffusion in Conway units. No significant difference has been found between the two methods, but the microdiffusion enables the concentration of nitrogen to smaller volumes and each sample has its own distillation unit, thus avoiding contamination between samples. Therefore microdiffusion was recommended for sample preparation for15N analysis. © 1974 The Williams & Wilkins Co. © 1974 The Williams & Wilkins Co.