Evaluation of soil C-14 data for estimating inert organic matter in the RothC model

• Published in: Radiocarbon Vol. 49; no. 2
• Main Authors: Rethemeyer, J., Grootes, P.M., Brodowski, S., Ludwig, B.
• Format: Journal Article
• Language: English
• Published: United States 01.07.2007
• Subjects: 01 COAL, LIGNITE, AND PEAT; CARBON; CARBON 14; CHEMICAL ANALYSIS; CONCENTRATION RATIO; FOSSIL FUELS; LIGNITE; MASS BALANCE; ORGANIC MATTER; SOILS
• ISSN: 0033-8222; 1945-5755
• DOI: 10.1017/S0033822200042934

Changes in soil organic carbon stocks were simulated with the Rothamsted carbon (RothC) model. We evaluated the calculation of a major input variable, the amount of inert organic matter (IOM), using measurable data. Three different approaches for quantifying IOM were applied to soils with mainly recent organic matter and with carbon contribution from fossil fuels: 1) IOM estimation via total soil organic carbon (SOC); 2) through bulk soil radiocarbon and a mass balance; and 3) by quantifying the portion of black carbon via a specific marker. The results were highly variable in the soil containing lignite-derived carbon and ranged from 8% to 52% inert carbon of total SOC, while nearly similar amounts of 5% to 8% were determined in the soil with mainly recent organic matter. We simulated carbon dynamics in both soils using the 3 approaches for quantifying IOM in combination with carbon inputs derived from measured crop yields. In the soil with recent organic matter, all approaches gave a nearly similar good agreement between measured and modeled data, while in the soil with a fossil carbon admixture, only the C-14 approach was successful in matching the measured data. Although C-14 was useful for initializing RothC, care should be taken when interpreting SOC dynamics in soils containing carbon from fossil fuels, since these reflect the contribution from both natural and anthropogenic carbon sources.