CENTURY ECOSYSTEM CENTURY ECOSYSTEM MODELMODEL

Introduction to CENTURYIntroduction to CENTURY

WHY CENTURYWHY CENTURY

Evaluate Effects of Environmental Evaluate Effects of Environmental ChangeChange

Evaluate Changes in ManagementEvaluate Changes in Management

What is CENTURY?What is CENTURY?

Simple Ecosystem ModelSimple Ecosystem ModelSoil Organic MatterSoil Organic Matter

Plant ProductionPlant ProductionHydrologicalHydrological

Nutrient CycleNutrient Cycle

Why CENTURY was developedWhy CENTURY was developed

From early experience (1970’s) of From early experience (1970’s) of attempting to model everything (e.g. IBP) attempting to model everything (e.g. IBP) an understanding of the inherent an understanding of the inherent problems of scaling processes and problems of scaling processes and components within appropriate time and components within appropriate time and spatial scales for a specific set of spatial scales for a specific set of questions or hypothesesquestions or hypotheses

MODEL DEVELOPMENTMODEL DEVELOPMENT

•Development of CENTURY of biogeochemical cycles of C, N, P, Development of CENTURY of biogeochemical cycles of C, N, P, and S for various ecosystem found globally was undertaken in and S for various ecosystem found globally was undertaken in order to provide adequate process-level representation of key order to provide adequate process-level representation of key transfers of material from critical ecosystem components.transfers of material from critical ecosystem components.

•Soil Organic Matter (SOM) was the focus of the model Soil Organic Matter (SOM) was the focus of the model development because of the integration of ecosystem processes development because of the integration of ecosystem processes and environmental changes which is represented in SOM.and environmental changes which is represented in SOM.

•Environmental and land management factors can be easily Environmental and land management factors can be easily incorporated into the simulations of SOM development.incorporated into the simulations of SOM development.

•Input parameters be meaningful in ecological terms and easily Input parameters be meaningful in ecological terms and easily acquired from existing data bases or experimentally determined. acquired from existing data bases or experimentally determined.

MODEL STRUCTUREMODEL STRUCTURE

Structure based on turnover rates of SOM poolsStructure based on turnover rates of SOM pools

THREE TYPES OF SOM POOLSTHREE TYPES OF SOM POOLS

ACTIVE: Live microbes and their by-ACTIVE: Live microbes and their by- products products (2 to 5 year turnover)(2 to 5 year turnover)

SLOW: Physically and chemically protected SLOW: Physically and chemically protected (20 to 50 years turnovers)(20 to 50 years turnovers)

PASSIVE: Physically protected or chemically resistant PASSIVE: Physically protected or chemically resistant SOM SOM

(800 to 1200 year turnover)(800 to 1200 year turnover)

MODEL CONTROLSMODEL CONTROLS

Monthly inputs of temperature and rainfallMonthly inputs of temperature and rainfall

Soil properties easily definedSoil properties easily defined

Plant system controlled by T, HPlant system controlled by T, H22O, and nutrient O, and nutrient

availabilityavailability

Land management practices modifies ecosystem Land management practices modifies ecosystem processesprocesses

Hydrological input-output processes representedHydrological input-output processes represented

WHY MODEL?WHY MODEL?

•Provides a conceptual framework from Provides a conceptual framework from which to pose hypotheseswhich to pose hypotheses

•Provides a mechanism to test a set of Provides a mechanism to test a set of complex hypothesescomplex hypotheses

•Provides insight into methods of Provides insight into methods of field/lab testing model predictionsfield/lab testing model predictions

SUMMARYSUMMARY

•CENTURY IS A TOOL FOR ANALYSIS OF CENTURY IS A TOOL FOR ANALYSIS OF CONTROLS ON SOIL ORGANIC MATTER AND CONTROLS ON SOIL ORGANIC MATTER AND PRODUCTIVITYPRODUCTIVITY•SIMULATION RESULTS DEMONSTRATE HOW SIMULATION RESULTS DEMONSTRATE HOW INPROVED MANAGEMENT PRACTICES CAN INPROVED MANAGEMENT PRACTICES CAN ARREST ORGANCI MATTER LOSSES AND ARREST ORGANCI MATTER LOSSES AND IMPROVE DEGRADED SOILS THROUGH:IMPROVE DEGRADED SOILS THROUGH:

Higher yielding varietiesHigher yielding varietiesReduced soil disturbanceReduced soil disturbanceMaintenance of crop residuesMaintenance of crop residuesReplacement of nutrient lossesReplacement of nutrient losses

Overall flow diagram for the CENTURY model.

Flow diagram for the soil carbon submodel.

Impact of temperature and water on decomposition.

Impact of DEFAC and AET on decomposition.

Observed above ground NPP for various global sites vs. CENTURY modeled abiotic decomposition factor (DEFAC).

Flow diagram for the water flow submodel.

Flow diagram for the nitrogen submodel.

Impact of mineral N on soil C/N ratios for grasslands and forests.

Effect of initial litter N content on litter carbon and N mineralization.

Effect of soil texture on litter C and N mineralization.

Flow diagram for the phosphorus submodel.

Flow diagram for the grass/crop submodel.

Impact of soil water and temperature on plant production.

C/N of live shoots vs. biomass for grass/crop systems.

Flow diagram for forest submodel.

Live forest C/N ratio as a function of ratio of available plant N to potential plant N demand.

Allocation of N to trees vs. grass as a function of tree basal area and SITPOT.

Comparison of simulated and observed live biomass for (a) Kenya, (b) Lamto, (c) Mexico, and (d) Thailand sites.

Comparison of observed and simulated aboveground plant production.

Comparison of observed and simulated soil C (0-30 cm) and soil N (0-30 cm).

Comparison of simulated and observed soil (a) C and (b) N.

Observed vs. simulated soil C for different treatments.

Flow diagram for DAYCENT.

Nitrification and denitrification N gas flow diagram. (Del Grosso et al. 2001)

NH4

+

Nitrification

NO3-

Ngasden

N Gas SubmodelH2Osoil, TsoilTexture, pH

D/DoPPT

H2Osoil, CTexture

D/DoNO3:C

= controlitalics = processNgasnit = N gas flux from nitrificationNgasden = N gas flux from denitrificationD/Do = index of gas diffusivity in soilPPT = precipitationC = labile carbon

N2O

NOx

N2

Ngasnit

Denitrification

MineralizationN inputs

DAYCENT soil water flow diagram.

Comparison of observed vs. simulated WFPS.

Comparison of observed vs. simulated soil temperature.

Comparison of observed vs. simulated N2O flux.

Comparison of observed and simulated NOx flux.

Comparison of observed and simulated H2O and NOx fluxes.

Comparison of simulated changes in soil C, integrated C equivalents of N2O emissions and net C for a conventional tillage winter wheat/fallow system (ww), no till winter wheat fallow (wwnt),

irrigated corn, and reversion to native grass for 25 year periods following 75 years of conventional till winter wheat/fallow land use. Negative values represent uptake of greenhouse

gases by the soil. (From Del Grosso et al. 2001)

Soil C

-2000

-1500

-1000

-500

0

500

gC

m-2

25y

rs-1

0-25yrs

26-50yrs

51-75yrs

76-100yrs

N2O C Equivalents

0

250

500

750g

C m

-2 2

5yrs

-1

Net C = Csystem + CN2O + CNfert

-1200

-900

-600

-300

0

300

corn ww wwnt grass

gC

m-2

25y

rs-1

The CENTURY model environment showing the relationship between programs and the file structure.