CENTURY-simulated versus observed winter wheat yield for Weld County, Colorado from 1930 through 1990.

Figure 13.3 shows the simulation of winter wheat crop yields from 1920 to 1990 for Weld County in eastern Colorado. The model included the change in cultivation practices, crop varieties, and fertilization levels in order to simulate the changes in crop yields during that time period. This model allows the tracking of long term changes in soil or ganic matter and nutrient cycling, and projections of the impact of new land use prac tices such as the Conservation Reserve Program on agroecosystem dynamics. Most of the current global ecosystem models are in the process of being modified to incorporate the effect of land use practices on natural and managed ecosystems.