Effects of different methods of acid hydrolysis on the nitrogen distribution in two soils

Summary An inorganic (Bainsville) and an organic (Farnham) soil were hydrolyzed by continuous and stepwise hydrolysis with hot 3N HCl for 1, 2, 3, 4, 11, 15, 18 and 24 h and continuously with hot 6N HCl for 24 h. The following nitrogen forms were determined: total N, hydrolyzable-N, amino acid-N, amino sugar-N and ammonia-N. Proportions of ‘unknown’ N were computed from these data. Continuous hydrolysis with 3N HCl yielded more amino acid-N and less ‘unknown’ N than did stepwise hydrolysis with the same acid strength. But continuous hydrolysis for 24 h with 6N HCl produced more amino acid-N and less ‘unknown’ N than did hydrolysis with 3N HCl by either method. It was estimated that 33 and 54% of the total N in the inorganic and organic soil, respectively, was protein-N. The ‘unknown’ N in the inorganic and organic soil constituted 51 and 37% of the total N, respectively. From our work it appears that the ‘unknown’ N is not proteinaceous. It can be readily degraded chemically and microbiologically to NH₃ and N-gases. More attention needs to be given to identifying the ‘unknown’ N which constitutes a large portion of the total soil-N. A more adequate knowledge of the chemical constitution of the ‘unknown’ soil N may lead to the development of technologies that will make more efficient use of the N in soils.