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CGMS/WOFOST model principles

CGMS/WOFOST model principles. Bernard TYCHON University of Liège Department of Environmental Sciences and Management B-6700 Arlon Belgium Presentation based on Decrem, Gommes, Supit and van Diepen’s documents. Training on the Mars Crop Yield Forecasting System – IPSC – JRC

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CGMS/WOFOST model principles

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  1. CGMS/WOFOST model principles Bernard TYCHON University of Liège Department of Environmental Sciences and Management B-6700 Arlon Belgium Presentation based on Decrem, Gommes, Supit and van Diepen’s documents. Training on the Mars Crop Yield Forecasting System – IPSC – JRC Ispra, Italy, 29-30/11/2005

  2. WOFOST = model developed by the Centre for World Food Studies in Wageningen, the Netherlands. • WOFOST is a dynamic, mechanistic model that simulates crop growth on the basis of the underlying processes, such as photosynthesis, respirationetc. • CGMS = spatial version of WOFOST

  3. The WOFOST approach • WOFOST simulates the crop life cycle from sowing to maturity. • Meteorological data (rain, temperature, wind speed, global radiation, air humidity) are needed as input. • Model parameters include soil moisture content at field capacity and wilting point, and other parameters on saturated water flow. Also information on site-specific crop management is requested. • The crop growth model includes parameters for European crops (Wheat, Grain Maize, Barley, Rice, Sugar Beet, Potato, Field Bean, Soy Bean, Oilseed Rape, Sunflower, etc.) and for tropical crops (Sorghum, Millet, Cassava, Groundnut, Sweet potato...).

  4. 1. Production levels WOFOST is able to predict yields in several production levels: • Production level 1: Potential (radiation and T° limited) • Production level 2: Water limited • Production level 3: Nutrient limited(not used in CGMS)

  5. Production level 1: Potential (radiation and temperature limited) • Growth occurs in conditions with abundant plant nutrients and water all the time. • The growth rate of vegetation is determined by weather conditionsvery intensively managed irrigated crops. • The only inputs to the model are temperature and radiation.

  6. Production level 2: Water limited • Growth is limited by water shortage at least part of the timeintensively managed dryland crops. • The model must determine water stress and its effect on the photosynthetic and growth processes. • Beside temperature and radiation, another input to the model is precipitation.

  7. Production level 3: Nutrient limited • Growth is limited, at least part of the time, by shortage of nitrogen (N), phosphorus (P) or potassium (K), and water or weather at other times.  usualdryland crops even if ‘well-fertilized’. • The model must determine soil nutrients dynamics, plant uptake, nutrient use in the plant, and effects of nutrient stress on photosynthesis, partition and growth.

  8. 2. Functionality Flow chart of the WOFOST model

  9. Weather • The meteorological data used by WOFOST are: • maximum temperature, • minimum temperature, • global radiation, • wind speed, • vapour pressure, • rainfall. • The Penman method is used to calculate the evapotranspiration. • The global radiation is estimated using the Ångström formula when no actual data are available. The Ångström formula uses the sunshine duration as input.

  10. Crop growth (1) • Crop growth depends on the daily net assimilation, which depends on the intercepted light. • Reduction of the transpiration due to water stress results in a reduced production of assimilates. • The assimilates are partitioned over the various plant organs.

  11. Crop growth (2) Detailed flow chart of the crop growth simulated by WOFOST

  12. Interception of sunlight • Solar radiation at top of canopy • Solar radiation within canopy • Intercepted radiation • CO2 assimilation

  13. Maintenance respiration Propotional with • Biomass of living plant organs • Maintenance coefficient per plant organ • Temperature (Q10 factor : doubling with 10°C) (uses 15 – 30 % of all assimilates)

  14. Growth respiration Depend on : • Conversion coefficient per plant organ • Partitioning of assimilates over organs (uses 30 - 40% of all assimilates)

  15. Partitioning of assimilates and development stages

  16. Soil water balance (1) • A crop growth model also has to keep track of the soil moisture content to determine when and to what degree a crop is exposed to water stress. • WOFOST uses a water balance, which compares incoming water in the root zone with outgoing water and quantifies the difference between the two as a change in the soil moisture content.

  17. Soil water balance (2) Schematic representa-tion of the different components of the WOFOST soil water balance Bucket model, one layer

  18. Nutrient use (not used in CGMS) • Influence of nutrients (nitrogen, phosphate and potassium) on the yield is calculated on a yearly basis. • First the potential supplies of nitrogen, phosphorus and potassium are calculated. • In a second step, the actual uptake of each nutrient is calculated as a function of the potential supply of that nutrient, in order to obtain a yield estimate.

  19. 3. Summary of data requirements • Soil properties: horizon thickness, upper and lower limits of volumetric water content, volumetric water at saturation, hydraulic conductivity at saturation. • Daily weather data: radiation, precipitation, max/min temperatures, wind speed, and relative air humidity. • Crop parameters: temperature sums, photoperiod response, yield components, … • Initial conditions: water content, total nitrogen, phosphorus and potassium. • Management conditions: sowing and harvest dates.

  20. Inputs/outputs of the WOFOST model Meteo data Meteonetwork Water balance parameters Agro-meteorological model (WOFOST) Yield (kg/ha) Crops Reference parameters Soils Inputs Outputs

  21. Some results

  22. Applications of WOFOST/CGMS

  23. Spatial version of WOFOST model : the EU-Crop Growth Monitoring System (CGMS) Vegetation index Remote sensing Water balance parameters Production Meteo data Meteonetwork Agro-meteorological model WOFOST Yield function Crops Reference data Soils Area Current agricultural data Agricultural statistics District yield

  24. Relation between Evapotranspiration and assimilation [F(mesophyll resistance)] 4. Comparison with AGROMETSHELL (FAO)

  25. District Yield Agricultural statistics 2002 1985 1987 District ETA NDVI or other grid ETA grid Station water balance

  26. 5. A final warning • A more complex model does not necessary means better results than a simpler model. • As each parameter estimate and process formulation has its own inaccuracy, these errors accumulate in the prediction of final yield. • The model must be validated over the expected range of inputs, just like a statistical model. • Expertise is still required for a good use of WOFOST/CGMS as well as for AGROMETSHELL

  27. More information • http://agrifish.jrc.it/marsstat/Crop%5FYield%5FForecasting/METAMP/ • http://www.supit.net/

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