SIMULATING TRENDS IN SOIL ORGANIC-CARBON IN LONG-TERM EXPERIMENTS USING THE CENTURY MODEL

This paper describes Century Soil Organic Matter (SOM) Model simulatio ns of seven long-term data sets that are the subject of this special i ssue. We found that Century successfully simulates SOM C across a vari ety of land use and climate types. Simulations of SOM were most succes sful in grass and crop systems. This exercise highlights a structural limitation of Century in simulating SOM in a forest with a developed l itter layer. Simulations of tree biomass distributions, however, were generally successful. The model failed to capture extreme values of yi eld and N offtake, although annual averages were quite similar between observations and simulations, leading to reasonable estimates of SOM C. Average yields and SOM were generally higher in amended treatments or rotations including an N-fixing component such as alfalfa. The mode l successfully predicted SOM dynamics across climates, land use types, and treatments. This suggests that Century is a useful tool for ecosy stem studies, particularly those focused on SOM dynamics. (C) 1997 Els evier Science B.V.