FACTOR AFFECTING THE ACCURACY OF THE CARBONDATING METHOD IN SOIL HUMUS STUDIES

Abstract

The effect of isotopic fractionation, nuclear-bomb-produced C14, and precision of analytical techniques employed in studying soil humus, on the accuracy of the carbon-dating method as applied to soil science was investigated. The effect of re-use of soil CO2 by plants is discussed. C14 fractionation, calculated from C13/C12, was constant for several soils and humic fractions, and necessitated subtracting about 115 yr. from each measured mean residence time (m.r.t.). No apparent error has so far resulted from the increased incorporation of nuclear-bomb-produced C14 by plants. The possible error arising from lack of precision of the analytical techniques employed in carbon-dating studies on soil humus was relatively small, and was not considered a limiting factor to this type of study. Comparison of C13 data from plant material, soil humus, and Solenhofen limestone indicated that microorganisms do not discriminate between carbon isotopes during decomposition of organic matter.