Steps in Applying Century V

The information required by the CENTURY model can be considered under two categories, namely:

• Site characteristics data, which is related to the type of land mapping unit or land facet and the type of ecosystem sustained by such land unit

• Data on variables necessary for the parameterization of the model for the selected ecosystem: forest, grassland and agricultural land

Data input The following data are required for the model, which are site specific for the region and ecosystem selected:

• Mean monthly precipitation

• Maximum and minimum temperature

• Content of lignin in the plant material

• Content of N, P and S in the plant material

• Initial contents of total S, C, N and P in the soil

• Schedule of agricultural, livestock or forestry activities

• Levels and amounts of agricultural inputs used during the management cycle

• Production by land use types (crop yields or other outputs in tonnes per hectare)

• Date of disturbance (e.g. incidence of fire, clearings or other disturbing phenomena during the study period)

Parameterization of the model The first step is to define the major land category type, namely forest land, grassland and agricultural land, and the subsystem or project activity. Enter the specific information needed to parameterize the model for each ecosystem or project activity according to the modules. Module 1 Bulk density, number of soil layers or soil profile horizons, drainage pattern, permanent wilting point of the soil (lower limit of soil moisture for plant growth) and field capacity of the soil (moisture left is soil a few days after rain or irrigation) and pH.

Module 2 Labile organic C (g/m2), non-labile organic C (g/m2), C/N ratio per soil layer, initial inputs of plant residues (g/m2), C/N ratio of litter in soil, C/N ratio of the soil organic horizon and value of the C isotope in land cover (litter) (g/cm2). Module 3 Amount of C in foliage in the forest system, amount of N in foliage in the forest system, amount of C in fine and coarse branches, amount of N in fine and coarse branches, amount of C in fine and coarse roots, amount of N in fine and coarse roots and initial amount of C in dead material.

Linking data file structures and the CENTURY programme module CENTURY model consists of a large number of files as default values in the model, which can be used for generating outputs since these values have been generated and standardized for a range of ecosystems.

The model generates detailed outputs related to carbon, nitrogen and other components. The variables relevant for carbon sequestration are those that are related to fluxes of carbon in soil and CO2 release.

Steps in using the graphical user interface for CENTURY (V.5) model The following steps could be used for operationalization and running of the model:

Step 1: Open the CENTURY graphical user interface (GUI); a window displaying "Session history" and "Messages" appears along with "Quick steps" buttons, namely "Preferences" "Sites" "Management" "Output file" "Status" and "Run simulation" Step 2: Go to "Preferences" and set the project directories Step 3: Create a new site parameter or edit an existing one; the site parameters are listed above, under "Input" Step 4: Go to "Management" and specify the site management parameters by specifying general simulation information and defining the management block(s) Step 5: Go to "Output file" and select the output file format: choose either of the two output formats, namely NetCDF or spreadsheet (ASCII); NetCDF is more useful for gridded data and spreadsheet is more convenient to handle non-gridded data Step 6: Run the simulation

Step 7: Go to the "Result" menu and view/plot/browse/export the simulation results

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