MECHANISTIC SIMULATION OF VERTICAL-DISTRIBUTION OF CARBON CONCENTRATIONS AND RESIDENCE TIMES IN SOILS

We developed a numerical simulation model of the decay and vertical tr ansport of soil organic matter, Soil organic matter is divided into a number of compartments each with different decay rates but with simila r migration parameters. Decay has been represented with first-order pr ocesses. Two elementary forms of migration were explored: diffusive eq uations 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 a nd directly underground from roots. Profiles of total C content and C- 14 content were measured for a temperate forest silt loam soil. Simila r data for other forest soils, available in the literature, were also assembled, Statistical adjustment, through nonlinear regression, of de cay, migration, compartment configuration, and plant production parame ters, accurately simulated profiles of C and C-14, The rapidly decayin g compartment was successfully likened to the 50- to 2000-mu m particl e-size fraction, Convection rates of approximate to 0.3 mm yr(-1) and diffusion rates ranging from 1 to 15 cm(2) yr(-1) were obtained, Diffu sive processes appear to be preponderant relative to convection, The m odel has proven sensitive to differences between temperate and tropica l soils as well as textural variations.