Several studies have shown the satisfactory performance of the Century Model to study soil organic matter (SOM) for the climatic and edaphic conditions of Rio Grande do Sul. However, soil N stocks were usually overestimated in these simulations. The objective of this study was to parameterize the N cycle submodel of Century for a successful use in N dynamic studies in Southern Brazil. For the simulations, data from a long-term study site established in an Acrisol (Argissolo Vermelho distrófico) at EEA-UFRGS (Eldorado Agricultural Experiment Station - UFRGS) in 1985 were used. The initial parameterization included soil and climate properties, non-symbiotic N fixation inputs, N losses by volatilization and C/N ratios of plant residues that enter the slow and passive N pools of SOM. Century was run for a simulation period of 6,000 years to determine the steady state of soil total carbon and nitrogen stocks and the C and N soil compartments for conditions of Southern Brazilian grasslands (mesic biome/subhumid grassland). Subsequently, eight selected treatments (conventional and no-tillage managements, two crop systems and two N levels in factorial combination) were simulated according to historical soil management data, with appropriate changes in the cultivation parameter CLTEFF(2) (slow pool decomposition multiplier), which was affected by crop C inputs and tilling intensity. Additionally, an "enhanced cultivation effect" was included for two months after each plowing event in the conventional soil management schedules. This extension of the tilling effect resulted in a better adjustment of the soil C dynamics in the case of the conventional tillage system, reflecting the higher soil organic matter decomposition under the local conditions. In general, the estimates of the model with the above-mentioned parameterization agreed well with the field data measured in 1998. This indicates the Century model as a feasible tool for the planning and establishment of soil management strategies.
organic matter; soils of subtropical regions; soil management systems
