Modeling soil organic matter dynamics after conversion of native grassland to long-term continuous fallow using the CENTURY model

A long-term continuous fallow experiment provides a unique opportunity to test current approximations of soil organic matter dynamics, which are the basis of many models including the CENTURY model. This study was conducted to validate the CENTURY model by comparing the simulated results for a continuous fallow scenario to long-term measurements of soil organic carbon (SOC) in a 50-year continuous fallow field, located in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia. Experimental data were obtained for soil physical properties, SOC and nitrogen (N) contents for the top 20 cm of soil at the 50-year continuous fallow field and an adjacent native grassland field. All sampled soils were classified as fine-silty, mixed, frigid Pachic Hapludolls. Live and dead plant biomass, and plant roots collected at the native site were analyzed for C, N and lignin contents. These new experimental data were incorporated into the CENTURY model parameters. Following conversion of measured SOC values to dry-combustion equivalent and correction of simulation output for changes in bulk density, the CENTURY model successfully simulated SOC dynamics in the 50-year continuous fallow field. Comparison of observed and modeled SOC concentrations yielded an R² value of 0.96. (C) 2000 Elsevier Science B.V.