Simulation of Soil Carbon Dynamics with SALUS

Schulthess, U., H.P. Collins, D. Harris, E.A. Paul, and J.T. Ritchie

Presented at the All Scientist Meeting (1998-07-21 to 1998-07-22 )

Organic matter simulation models are typically used to simulate long-term dynamics of soil organic matter. The Century model, which runs on a daily time step, has been integrated into a crop simulation model, called SALUS (System Approach to Land Use Sustainability). SALUS runs on a daily time step. We tested the capabilities of SALUS to predict soil CO2 dynamics on a daily time step. The model was used to simulate soil carbon dynamics of a moldboard plowed (conventional) corn/soybean rotation. Results from an incubation study as well as 14C dating were used to initialize the carbon pool sizes and the decomposition parameters of the model. The laboratory derived decay constants were reduced by 20% for the depths below 25 cm.The model predicted trends in CO2-C evolution within a year quite well, although it tended to under predict CO2-C evolution during the summer months; it does not yet simulate root respiration. The tendency of SALUS to over predict CO2-C evolution in the fall is attributable to the fact that it does not consider a lag period until the residues are colonized and comminuted. In accordance with observed data, the model predicted a higher CO2-C evolution for 1994 as compared to 1993. The higher rates in 1994 were attributable to residues from the previous corn crop. In 1993, the previous crop was soybean. The model when run for two years with pool and flux rate data derived from laboratory measurements showed a slight accumulation of crop residues and an equivalent drop in the Cs.Return to Contents

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