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Mechanistic Simulation of Vertical Distribution of Carbon Concentrations and Residence Times in Soils

Station de Science du Sol, INRA, F78026 Versailles cedex

Jérôme Balesdent^*

Laboratoire de Biogéochimie Isotopique, INRA-UPMC, 4 Place Jussieu, Case 120, F75252 Paris cedex 05

*Corresponding author (balesden{at}ccr.jussieu.fr).

ABSTRACT

We developed a numerical simulation model of the decay and vertical transport of soil organic matter. Soil organic matter is divided into a number of compartments each with different decay rates but with similar migration parameters. Decay has been represented with first-order processes. Two elementary forms of migration were explored: diffusive equations represent transport through soil mixing whereas translational convection simulates movement within the liquid phase. Coefficients of decay, diffusion, and convection were taken to be uniform with depth. Carbon input is both through the surface in the form of litter fall and directly underground from roots. Profiles of total C content and ¹⁴C content were measured for a temperate forest silt loam soil. Similar data for other forest soils, available in the literature, were also assembled. Statistical adjustment, through nonlinear regression, of decay, migration, compartment configuration, and plant production parameters, accurately simulated profiles of C and ¹⁴C. The rapidly decaying compartment was successfully likened to the 50- to 2000-µm particle-size fraction. Convection rates of 0.3 mm yr^–1 and diffusion rates ranging from 1 to 15 cm² yr^–1 were obtained. Diffusive processes appear to be preponderant relative to convection. The model has proven sensitive to differences between temperate and tropical soils as well as textural variations.

Contribution from the Institut National de la Recherche Agronomique, France.

Received for publication May 24, 1994.