The use of radiocarbon dating of organic matter in the study of soil genesis

Abstract

Radiocarbon dating was used to study the nature and the stability of the organic matter in a range of Chernozemic soils (Borolls) from Saskatchewan. Two catenas, one cultivated, the other not, were studied in detail; the bottom soils of the uncultivated catena contained buried horizons. From the crest of the knoll to the depression, the mean residence time of the surface horizon of the cultivated catena decreased from 545 years before present (B.P.) to modern, the organic matter content increased and the percentage of hydrolyzable carbon decreased. The content of organic matter decreased but the mean residence time increased by 700 to 4,000 years in the B horizons. Two buried horizons located at different depths underneath the lower members of the uncultivated catena showed mean residence times of 5,950 and 8,410 years B.P. indicating that mass movement of soil had periodically occurred since the last glaciation. The 14C content of a field soil, measured by radiocarbon dating, was compared with the 14C distribution in fractions of another sample of the same soil after amendment with 14C-acetate and 350 days incubation in the laboratory. The artificially labelled soil accumulated more of the tracer in the acid hydrolyzable fractions than was found by radiocarbon dating the field soil. In turn, the distribution of soil nitrogen was more closely associated with the 14C than with the unlabelled carbon of the soil.