Estimation of Slow- and Fast-Cycling Soil Organic Carbon Pools from 6N HCl Hydrolysis
- 1 January 1996
- journal article
- Published by Cambridge University Press (CUP) in Radiocarbon
- Vol. 38 (2), 231-239
- https://doi.org/10.1017/s0033822200017604
Abstract
Acid hydrolysis is used to fractionate the soil organic carbon pool into relatively slow- and fast-cycling compartments on soils from Arizona, the Great Plains states and Michigan collected for carbon isotope tracer studies related to soil carbon sequestration, for studies of shifts in C3/C4 vegetation, and for “pre-bomb” soil-carbon inventories. Prior to hydrolysis, soil samples are first treated with cold 0.5–1N HCl to remove soil carbonates if necessary. Samples are then dispersed in a concentrated NaCl solution (ρ≍1.2 g cm-3) and floated plant fragments are skimmed off the surface. After rinsing and drying, all remaining recognizable plant fragments are picked from the soil under 20x magnification. Plant-free soils, and hot, 6N HCl acid-hydrolysis residue and hydrolyzate fractions are analyzed for carbon content, δ13C and 14C age, and the carbon distribution is verified within 1–2% by stable-carbon isotope mass balance. On average, the recalcitrant residue fraction is 1800 yr older and 2.6% more 13C-depleted than total soil organic carbon. A test of hydrolysis with fresh plant fragments produced as much as 71–76% in the acid-hydrolysis residue pool. Thus, if plant fragments are not largely removed prior to hydrolysis, the residue fraction may date much younger than it actually is.Keywords
This publication has 13 references indexed in Scilit:
- Carbon isotope dynamics of free-air CO2-enriched cotton and soilsAgricultural and Forest Meteorology, 1994
- Comparison of carbon dynamics in tropical and temperate soils using radiocarbon measurementsGlobal Biogeochemical Cycles, 1993
- Particulate Soil Organic‐Matter Changes across a Grassland Cultivation SequenceSoil Science Society of America Journal, 1992
- Stable Carbon Isotope Ratios of Natural Materials: II. Atmospheric, Terrestrial, Marine, and Freshwater EnvironmentsPublished by Elsevier BV ,1991
- Analysis of Factors Controlling Soil Organic Matter Levels in Great Plains GrasslandsSoil Science Society of America Journal, 1987
- Organo‐Mineral Complexes and Their Study by Radiocarbon DatingSoil Science Society of America Journal, 1984
- Soil radiocarbon analysis and soil datingSurveys in Geophysics, 1977
- The Use of Radiocarbon Dating of Organic Matter in the Study of Soil GenesisSoil Science Society of America Journal, 1974
- The distribution of the stable carbon isotope (13C/12C) in fractions of soil organic matterGeoderma, 1974
- FACTOR AFFECTING THE ACCURACY OF THE CARBONDATING METHOD IN SOIL HUMUS STUDIESSoil Science, 1967