The nitrogen distribution in soils formed under widely differing climatic conditions

The chemistry of soil organic nitrogen: a review

“…Along the same lines, reported that in the 15 N-NMR spectrum of 15 N-labelled humic acid, 86.4% of the total area is due to amide/peptide, 4.3% to aliphatic amines, 3.9% to aliphatic and/or aromatic amines, and only 5.4% to pyrrole N. Similarly Knicker et al (1993) stated that 85% of the signal intensity in 15 N-NMR spectra of 15 N-enriched composts and recently formed humic materials is due to amide/peptide and that no signals in the range typical of heteroatomic N compounds were detected. In a more recent study, (Sowden et al 1977), but 15 N NMR of 15 N-labelled soils and humic substances revealed a protein content of 85% (Knicker et al 1993). Similarly, on the basis of chemical techniques measuring UH-N and NH-N, between 27% and 34% of the total N appears to be heterocyclic, compared to only 5% to 10% indicated by 15 N NMR.…”

“…If it were possible to stimulate the reduction of NO 3 -to NH 3 and its incorporation into organic matter (reaction 4), large N losses resulting from leaching or denitrification could be prevented. Sowden et al (1977) determined the distribution of the major N compounds in samples taken from soils formed under widely different climatic and geological conditions on the earth's surface. The soil samples came from arctic, subarctic, cool temperate, subtropical, and tropical regions.…”

“…All samples were hydrolyzed and analyzed by the same methods, which provided a type of uniformity which had not been attained before, and made it possible to gain new insights into the distribution of N in soils. Definitions of the different classes of N compounds as employed by Sowden et al (1977) are listed in Table 1. While the total N content of the samples analyzed varied from 0.01% to 1.61% , the proportions of total N that could be hydrolyzed by hot 6 M HCl were quite similar (84.2% to 88.9%).…”

“…The amino acid composition of the soils investigated by Sowden et al (1977) was remarkably similar, except for the following differences: (1) tropical soils rich in amorphous aluminum (Al) silicates contained relatively high concentrations of acidic amino acids whereas arctic soils were low in these amino acids; (2) there were smaller amounts of basic amino acids in the tropical soils then in the other soils. This is in agreement with the observation that acidic amino acids are concentrated in particle-size fractions rich in noncrystalline Al compounds (Schnitzer and Kodama 1992).…”

“…Glucosamine was always present in greater amounts than galactosamine. Sowden et al (1977) compared the mean amino acid composition of the soils analyzed with those of algae, bacteria, fungi, and yeasts, and found that the amino acid composition of soils was most similar to that of bacteria. This indicates that in soils microbes play a major role in the synthesis of proteins, peptides, and amino acids from plant and animal residues.…”