Under the Hood
The Cropping System Model (CSM) is structured in a modular format in which components separate along scientific discipline lines and have interfaces which allow replacement or addition of modules. CSM now incorporates all crop models as modules using a single soil module and a single weather module. The new cropping system model now contains models of 40+ crops derived from the original SOYGRO, PNUTGRO, CERES-Maize, and CERES-Wheat crop growth models.
The following schematic illustrates the connection between the primary and secondary modules of the CSM. The main program controls all the timing for the model, while the Land Unit module is used to control processing and data transfer between all primary modules.
DSSAT Cropping System Model schematic
The Management module processes user inputs describing crop management. This includes plantings, irrigations, fertilizer applications, tillage events, addition of organic material (residues or manure) and harvests. The module thus is key in processing information associated with what are considered “treatments” in field experiments. The module includes provisions for rule-based automatic management such as to control planting dates when a given date and soil temperature threshold are attained.
Further information on how crop management is simulated may be accessed here.
The Soil module deals with simulation of the dynamics of soil constituents including:
- Soil water
- Inorganic soil N
- Inorganic soil P
- Inorganic soil K
- Soil organic matter module
- CENTURY soil organic matter module – A SOM–residue module from the CENTURY model was incorporated in the DSSAT crop simulation models, and a residue layer was added on top of the soil. Modifications were also made in the senescence module of CROPGRO, a model within DSSAT, so that senesced material is now added daily to the soil. By incorporating the CENTURY SOM–residue module, DSSAT crop simulation models have become more suitable for simulating low-input systems and conducting long-term sustainability analyses.
- CERES Soil Organic matter module
- Greenhouse Gas Emissions Modules
- Ceres Denitrification
- DayCent Denitrification
- N-gas emissions
- Methane emissions
- Surface organic mulch
- Flood N dynamics
Detailed information on soil process modeling is here.
The Weather module inputs daily weather data and also can generate long term (e.g., 30-year) series of daily weather data that reproduce the statistical properties of a shorter series of weather years. The minimum daily weather data required are solar radiation, minimum and maximum air temperatures, and precipitation. However, for more accurate estimation of evapotranspiration, humidity (e.g., as daily mean dewpoint temperature) and wind speed are required.
Further information on the module is here and on weather data sources and issues is here.
The Soil-Plant-Atmosphere module (SPAM) module deals with competition for light and water among the soil, plants, and atmosphere. It models evapotranspiration (ET) and soil temperatures.
Detailed information is available here.
The original crop models of DSSAT were CERES-Maize, CERES-Wheat, SOYGRO, and PNUTGRO. These models evolved over time from many independent models to become a single agricultural systems model that encompasses all the original crop models as individual crop modules (Jones et al., 2001).
Information on specific crops is accessible here.