Purines and Pyrimidines in Soils and Humic Substances

Purines and pyrimidines were determined by ion‐exclusion chromatography in soils and humic substances of widely differing origins. Concentrations of purines + pyrimidines ranged from 20.9 to 137.7 µg per g of dry soils, from 210.8 to 810.0 µg per g of dry, ash‐free humic acids, and from 294.3 to 1086.6 µg per g of dry, ash‐free fulvic acids. Quantitatively the distribution in soils was as follows: guanine > cytosine > adenine > thymine > uracil. Humic acids were richer in guanine and adenine but poorer in cytosine, thymine and uracil than were fulvic acids. Guanine + cytosine over adenine + thymine ratios for soils and humic substances averaged > 2 and methyl cytosine was not detected, suggesting a microbial DNA origin for the nucleic acid bases extracted. The proportion of total N in purines + pyrimidines was inversely proportional to the total N content. An average 3.3% of the total N in the inorganic soils but only 0.3% of the total N in the organic soils analyzed were found to occur in nucleic acid bases.