The fixed parameters for the Century Model are not really fixed, rather they vary with the general type of biome to be simulated. Crop, grass, forest will have different fixed parameter sets. Several versions of these sets are provided with the Century distribution files.
| Parameter | Description | Units | Valid Values | Default Values |
| ADEP(1) through ADEP(10) | Default depths of soil layers (only NLAYER values used). | cm | > 0 | |
| AGPPA | Intercept parameter in the equation estimating potential aboveground biomass production for calculation of root/shoot ratio (g/m2/y) (used only if FRTC(1) = 0). | |||
| AGPPB | Slope parameter in the equation estimating potential aboveground biomass production for calculation of root/shoot ratio (g/m2/y/cm) (used only if FRTC(1) = 0). NOTE - AGPPB is multiplied by annual precipitation (cm). | |||
| ANEREF(1) | Ratio of rain/potential evapotranspiration below which there is no negative impact of soil anaerobic conditions on decomposition. | |||
| ANEREF(2) | Ratio of rain/potential evapotranspiration above which there is maximum negative impact of soil anaerobic conditions on decomposition. | |||
| ANEREF(3) | Minimum value of the impact of soil anaerobic conditions on decomposition; functions as a multiplier for the maximum decomposition rate. | |||
| ANIMPT | Slope term used to vary the impact of soil anaerobic conditions on decomposition flows to the passive soil organic matter pool. | |||
| AWTL(1) through AWTL(10) | Factor for transpiration loss for each soil layer (only NLAYER values used). Indicates which fraction of the water available for transpiration can be extracted by the roots, and is proportional to the root density in the layer. | |||
| BGPPA | Intercept parameter in the equation estimating potential belowground biomass production for calculation of root/shoot ratio (g/m2/y) (used only if FRTC(1) = 0 (g/m2/y). | |||
| BGPPB | Slope parameter in the equation estimating potential belowground biomass production for calculation of root/shoot ratio (g/m2/y) (used only if FRTC(1) = 0). NOTE - BGPPB is multiplied by annual precipitation (cm). | |||
| CO2PPM(1) | Initial parts per million for CO2 effect. | ppm | ||
| CO2PPM(2) | Final parts per million for CO2 effect. | ppm | ||
| CO2RMP | Flag indicating whether
CO2 effect should be: 0 = step function 1 = ramp function |
0 or 1 | ||
| DAMR(1,1), DAMR(1,2), DAMR(1,3) | Fraction of surface N, P, and S, respectively, absorbed by residue. | 0.0 to 1.0 | ||
| DAMR(2,1), DAMR(2,2), DAMR(2,3) | Fraction of soil N, P, and S, respectively, absorbed by residue. | 0.0 to 1.0 | ||
| DAMRMN(1), DAMRMN(2), DAMRMN(3) | Minimum ratio of C to N, P, and S, respectively, allowed in residue after direct absorption. | |||
| DEC1(1) , DEC1(2) | Structural decomposition rate for surface and soil, respectively; the fraction of the pool that turns over each year. | 0.0 to 1.0 | ||
| DEC2(1) , DEC2(2) | Metabolic decomposition rate for surface and soil, respectively; the fraction of the pool that turns over each year. | 0.0 to 1.0 | ||
| DEC3(1) , DEC3(2) | Decomposition rate of surface and soil organic matter, respectively, with active turnover; the fraction of the pool that turns over each year. | 0.0 to 1.0 | ||
| DEC4 | Decomposition rate of soil organic matter with slow turnover, the fraction of the pool that turns over each year. | 0.0 to 1.0 | ||
| DEC5 | Decomposition rate of soil organic matter with intermediate turnover, the fraction of the pool that turns over each year. | 0.0 to 1.0 | ||
| DECK5 | Available soil water content at which shoot and root death rates are half maximum. | cm | ||
| DLIGDF | Difference in delta 13C for lignin compared to whole plant delta 13C. | |||
| DRESP | Discrimination factor for 13C during decomposition of organic matter due to microbial respiration. | |||
| EDEPTH | Initial and minimum depth of the simulation soil layer where C , N , P , and S dynamics are calculated. The actual simulation soil depth can change with erosion and deposition. | cm | 20 | 20 |
| ELITST | Effect of litter on soil temperature relative to live and standing dead biomass. | 0.4 | ||
| ENRICH | The enrichment factor for SOM losses due to erosion. This factor reflects the variation in SOM with depth through the simulation layer. It is common for SOM density (g/cm3) to decrease with depth below the surface organic horizons. | 1.0 | ||
| FAVAIL(1), FAVAIL(3) | Fraction of N and S, respectively, available per month to plants. The P fraction, FAVAIL(2), is computed. | 0.0 to 1.0 | ||
| FAVAIL(4), FAVAIL(5) | Minimum and maximum fraction, respectively, of P available per month to plants. | 0.0 to 1.0 | ||
| FAVAIL(6) | Mineral N in surface layer corresponding to maximum fraction of P available. | g/m2 | 0.0 to 1.0 | |
| FLEACH(1), FLEACH(2) | Intercept and slope, respectively, for a normal month to compute the fraction of MINERL N, P, and S which will leach to the next layer when there is a saturated water flow. Normal leaching is a function of sand content. | 0.6 and 0.4 | ||
| FLEACH(3), FLEACH(4) , FLEACH(5) | Leaching fraction multiplier for N, P, and S, respectively, used to compute the fraction of MINERL N, P, and S which will leach to the next layer when there is a saturated water flow; normal leaching is a function of sand content. Normal leaching is a function of sand content . | 0.0 to 1.0 |
(3) = 0.95 (4) = 0.0 (5) = 0.1 |
|
| FWLOSS(1) | Scaling factor for interception and evaporation of precipitation by live and standing dead biomass. | 0.0 to 1.0 | 1.0 | |
| FWLOSS(2) | Scaling factor for bare soil evaporation of precipitation. | 0.0 to 1.0 | 1.0 | |
| FWLOSS(3) | Scaling factor for transpiration water loss. | 1.0 | ||
| FWLOSS(4) | Scaling factor for potential evapotranspiration. | 0.8 | ||
| FXMCA , FXMCB | Intercept and slope, respectively, for effect of biomass on non-symbiotic soil N fixation. Used only when NSNFIX = 1. | -0.125 and 0.005 | ||
| FXMXS | Maximum monthly non-symbiotic soil N -fixation rate (reduced by effect of N : P ratio, used when NSNFIX = 1). | 0.35 | ||
| FXNPB | N / P control for N -fixation based on availability of top soil layer (used when NSNFIX = 1). | 7.0 | ||
| GREMB | Grazing effect multiplier for types 4, 5, 6. | |||
| IDEF | Flag for method of computing water
effect on decomposition: 1 = Use the relative water content of soil in the simulation depth range of the soil. 2 = Use a function of the ratio of rainfall to potential evapotranspiration (AVH2O(3) + RAIN + IRRACT) / PET: 1 / (exp(ratio * -8.5) * 30 +
1). |
1 or 2 | 1 | |
| LHZF(1) | The fraction of the active soil C pool (SOM1CI(2,*)) that the lower soil horizon active C pool will be initialized to. | 0.2 | ||
| LHZF(2) | The fraction of the slow soil C pool (SOM2CI(*)) that the lower soil horizon slow C pool will be initialized to. | 0.4 | ||
| LHZF(3) | The fraction of the passive soil C pool (SOM3CI(*)) that the lower soil horizon passive C pool will be initialized to. | 0.8 | ||
| MINLCH | Critical water flow for leaching of minerals (cm of H2O leached from the bottom-most soil layer). | 0.1 | ||
| NSNFIX | Equals 1 if non-symbiotic N fixation should be based on N : P ratio in mineral pool, otherwise non-symbiotic N fixation is based on annual precipitation. | 0 or 1 | ||
| NTSPM | Number of time steps per month for the decomposition submodel. (Do not change this valiue!) | 4.0 | ||
| OMLECH(1) through OMLECH(3) |
OMLECH(1) and OMLECH(2) are the intercept and slope, respectively, in the linear influence of sand content upon the amount of organic C leaching from active SOM in the simulation layer. This effect of sand upon leaching is calculated as: effect = OMLECH(1) + OMLECH(2) * sand fractionOMLECH(3) specifies the maximum amount of water flowing out of the simulation layer that can leach organic C (cm month-1). Water flow above this amount has no effect on leaching of organic C. |
(1) = 0.03 (2) = 0.12 (3) = 1.9 |
||
| P1CO2A(1), P1CO2A(2) | Intercept parameter which controls flow from surface and soil organic matter, respectively, with fast turnover to CO2 (fraction of organic C lost to CO2 when there is no sand in the soil). | |||
| P1CO2B(1), P1CO2B(2) | Slope parameter which controls flow from surface and soil organic matter, respectively, with fast turnover to CO2 (slope is multiplied by the fraction sand content of the soil). | |||
| P2CO2 | Controls flow from soil organic matter with intermediate turnover to CO2 (fraction of organic C lost as CO2 during decomposition). | |||
| P3CO2 | Controls flow from soil organic matter with slow turnover rate to CO2 (fraction of C lost as CO2 during decomposition). | |||
| PABRES | Amount of residue which will give maximum direct absorption of N (g C /m2). | |||
| PCEMIC(X,E) | Maximum (X = 1) or minimum (X = 2) C/E ratio for surface microbial pool. Values for E are: N = 1, P = 2, S = 3. | |||
| PCEMIC(3,E) | Minimum E content of decomposing aboveground material, above which the C / E ratio of the surface microbes equals PCEMIC(2,E). Values for E are: N = 1, P = 2, S = 3. | |||
| PEFTXA , PEFTXB | Intercept and slope, respectively, for the linear regression equation to compute the effect of soil texture on the microbial decomposition rate. The intercept is the effect of texture when there is no sand in the soil. | |||
| PHESP(1) | Minimum pH for determining the effect of pH on the solubility of secondary P (flow of secondary P to mineral P ) (for TEXESP(2) = m * (pH input) + b, m and b calculated using these PHESP values). | |||
| PHESP(2) | Value of TEXESP(2), the solubility of secondary P , corresponding to minimum pH (/yr). | |||
| PHESP(3) | Maximum pH for determining effect on solubility of secondary P (flow of secondary P to mineral P ) (for TEXESP(2) = m * (pH input) + b, m and b calculated using these PHESP values). | |||
| PHESP(4) | Value TEXESP(2), the solubility of secondary P , corresponding to maximum pH (/yr). | |||
| PLIGST(1) | Effect of lignin on surface structural or fine branch and large wood decomposition. | |||
| PLIGST(2) | Effect of lignin on soil structural or coarse root decomposition. |
PMCO2(1) - Surface; controls flow from surface metabolic to CO2 (fraction of C lost as CO2 during decomposition).
PMCO2(2) - Soil; controls flow from soil metabolic to CO2 (fraction of C lost as CO2 during decomposition).
PMNSEC(1) - Slope for N ; controls the flow from mineral to secondary N (/yr).
PMNSEC(2) - Slope for P ; controls the flow from mineral to secondary P (/yr).
PMNSEC(3) - Slope for S ; controls the flow from mineral to secondary S (/yr).
PMNTMP - Effect of biomass on minimum surface temperature.
PMXBIO - Maximum dead biomass (standing dead + 10% litter) level for soil temperature calculation and for calculation of the potential negative effect on plant growth of physical obstruction by standing dead and litter.
PMXTMP - Effect of biomass on maximum surface temperature.
PPARMN(1) - N ; controls the flow from parent material to mineral compartment (fraction of parent material that flows to mineral N , P , and S ).
PPARMN(2) - P ; controls the flow from parent material to mineral compartment; used when TEXEPP(1) is not equal to 1 (fraction of parent material that flows to mineral N , P , and S ).
PPARMN(3) - S ; controls the flow from parent material to mineral compartment (fraction of parent material that flows to mineral N , P , and S ).
PPRPTS(1) - The minimum ratio of available water to PET which would completely limit production assuming water content is equal to 0. Valid Range: 0.0 to 1.0
PPRPTS(2) - The effect of water content on the intercept , allows the user to increase the value of the intercept and thereby increase the slope of the line.
PPRPTS(3) - The lowest ratio of available water to PET at which there is no restriction on production. Valid Range: 0.0 to 1.0
PS1CO2(1) - Surface; controls amount of CO2 loss when structural decomposes to SOM1.
PS1CO2(2) - Soil; controls amount of CO2 loss when structural decomposes to SOM1.
PS1S3(1) - Intercept for flow from soil organic matter with fast turnover to soil organic matter with slow turnover (fraction of C from SOM1C to SOM3C).
PS1S3(2) - Slope for the effect of clay on the control of the flow from soil organic matter with fast turnover to soil organic matter with slow turnover (fraction of C from SOM1C to SOM3C).
PS2S3(1) - Slope value which controls flow from soil organic matter with intermediate turnover to soil organic matter with slow turnover (fraction of C from SOM2C to SOM3C).
PS2S3(2) - Intercept value which controls flow from soil organic matter with intermediate turnover to soil organic matter with slow turnover (fraction of C from SOM2C to SOM3C).
PSECMN(1) - N ; controls the flow from secondary to mineral N.
PSECMN(2) - P ; controls the flow from secondary to mineral P.
PSECMN(3) - S ; controls the flow from secondary to mineral S.
PSECOC - Controls the flow from secondary to occluded P.
RAD1P(1,1) - Intercept used to calculate addition term for C / N ratio of slow SOM formed from surface active pool.
RAD1P(2,1) - Slope used to calculate addition term for C / N ratio of slow SOM formed from surface active pool.
RAD1P(3,1) - Minimum allowable C / N used to calculate addition term for C / N ratio of slow SOM formed from surface active pool.
RAD1P(1,2) - Intercept used to calculate addition term for C / P ratio of slow SOM formed from surface active pool.
RAD1P(2,2) - Slope used to calculate addition term for C / P ratio of slow SOM formed from surface active pool.
RAD1P(3,2) - Minimum allowable C / P used to calculate addition term for C / P ratio of slow SOM formed from surface active pool.
RAD1P(1,3) - Intercept used to calculate addition term for C / S ratio of slow SOM formed from surface active pool.
RAD1P(2,3) - Slope used to calculate addition term for C / S ratio of slow SOM formed from surface active pool.
RAD1P(3,3) - Minimum allowable C / S used to calculate addition term for C / S ratio of slow SOM formed from surface active pool.
RCESTR(1) - C / N ratio for structural material (fixed parameter value).
RCESTR(2) - C / P ratio for structural material (fixed parameter value).
RCESTR(3) - C / S ratio for structural material (fixed parameter value).
RICTRL - Root impact control term used for calculating the impact of root biomass on nutrient availability.
RIINT - Root impact intercept used for calculating the impact of root biomass on nutrient availability.
RSPLIG - Fraction of lignin flow (in structural decomposition) lost as CO2. Valid Range: 0.0 to 1.0
SEED - Random number generator seed value.
SPL(1) - Intercept parameter for metabolic (vs. structural) split. Valid Range: 0.0 to 1.0
SPL(2) - Slope parameter for metabolic split (fraction metabolic is a function of lignin to N ratio). Valid Range: 0.0 to 1.0
STRMAX(1) - Maximum amount of structural material in surface layer that will decompose in grams of carbon per square meter (g C /m2).
STRMAX(2) - Maximum amount of structural material belowground that will decompose in grams of carbon per square meter (g C /m2).
TEXEPP(1) - Texture effect on parent
P mineralization:
0 = use PPARMN(2) in the weathering equation
1 = include the effect of texture using the remaining TEXEPP values with the
arctangent function
Valid Values: 0 or 1
TEXEPP(2) - x location of inflection point used in determining texture effect on parent P mineralization.
TEXEPP(3) - y location of inflection point used in determining texture effect on parent P mineralization.
TEXEPP(4) - Step size (distance from the maximum point to the minimum point) used in determining texture effect on parent P mineralization.
TEXEPP(5) - Slope of the line at the inflection point used in determining texture effect on parent P mineralization.
TEXESP(1) - Texture effect on secondary
P flow to mineral
P: 0 = to use PSECMN(2) in the weathering equation
1 = include the effect of pH and sand content using the equation specified by
TEXESP(2) (a function of pH and PHESP(1-4)) and
TEXESP(3).
Valid Values: 0 or 1
TEXESP(3) - Slope value used in determining effect of sand content on secondary P flow to mineral P.
TEFF()
Monthly Century:
TEFF(1) - Intercept
TEFF(2) - slope
TEFF(3) - exponent (Q10) value
for determining the temperature component of
DEFAC, the decomposition factor. The equation is
The default values are: TEFF(1) = 0, TEFF(2) = 0.125, TEFF(3) = 0.07
Daily Century:
TEFF(1) - "x" location of inflection point
TEFF(2) - "y" location of inflection point
TEFF(3) - step size (distance from maximum point to minimum point)
TEFF(4) - slope of line at inflection point
The equation is
The default values are: TEFF(1) = 15.40, TEFF(2) = 11.75, TEFF(3) = 29.70, TEFF(4) = 0.031
TMELT(1) - Minimum temperature above which at least some snow will melt. Default value = 0.0.
TMELT(2) - Ratio between degrees above the minimum and centimeters of snow that will melt. . Default value = 0.02.
VARAT1(1,1) - Maximum C / N ratio for material entering SOM1.
VARAT1(2,1) - Minimum C / N ratio for material entering SOM1.
VARAT1(3,1) - Amount N present when minimum ratio applies.
VARAT1(1,2) - Maximum C / P ratio for material entering SOM1.
VARAT1(2,2) - Minimum C / P ratio for material entering SOM1.
VARAT1(3,2) - Amount P present when minimum ratio applies.
VARAT1(1,3) - Maximum C / S ratio for material entering SOM1.
VARAT1(2,3) - Minimum C / S ratio for material entering SOM1.
VARAT1(3,3) - Amount S present when minimum ratio applies.
VARAT2(1,1) - Maximum C / N ratio for material entering SOM2.
VARAT2(2,1) - Minimum C / N ratio for material entering SOM2.
VARAT2(3,1) - Amount N present when minimum ratio applies.
VARAT2(1,2) - Maximum C / P ratio for material entering SOM2.
VARAT2(2,2) - Minimum C / P ratio for material entering SOM2.
VARAT2(3,2) - Amount P present when minimum ratio applies.
VARAT2(1,3) - Maximum C / S ratio for material entering SOM2.
VARAT2(2,3) - Minimum C / S ratio for material entering SOM2.
VARAT2(3,3) - Amount S present when minimum ratio applies.
VARAT3(1,1) - Maximum C / N ratio for material entering SOM3.
VARAT3(2,1) - Minimum C / N ratio for material entering SOM3.
VARAT3(3,1) - Amount N present when minimum ratio applies.
VARAT3(1,2) - Maximum C / P ratio for material entering SOM3.
VARAT3(2,2) - Minimum C / P ratio for material entering SOM3.
VARAT3(3,2) - Amount P present when minimum ratio applies.
VARAT3(1,3) - Maximum C / S ratio for material entering SOM3.
VARAT3(2,3) - Minimum C / S ratio for material entering SOM3.
VARAT3(3,3) - Amount S present when minimum ratio applies.
VLOSSE - Fraction per year of excess N (i.e. N left in the soil after nutrient uptake by the plant) which is volatilized. Valid Range: 0.0 to 1.0 (Monthly Century only.) Default value = 0.02.
VLOSSG - Fraction per month of gross N mineralization which is volatilized. Valid Range: 0.0 to 1.0 (Monthly Century only.) Default value = 0.01.
About the Model Internal Parameterization