Modeling organic carbon and carbon - mediated soil processes in DSSAT v 4 . 5

Cropping systems models have evolved over the last four decades in response to the demand for modeling to address more complex questions, including issues on sustainable production, climate change, and environmental impacts. Early models, which were used primarily for yield gap analysis, have increased in complexity to include not only nutrient and water deficiencies, but also pest and disease damage and processes affecting soil nutrient dynamics. This is the case in the CSM (Cropping System Model) within DSSAT (Decision Support System for Agrotechnology Transfer). This package was developed from various models of individual crops beginning about 25 years ago into one that now has over 25 crops integrated into one program that share many components in a modular format. This modular structure was intended to facilitate incorporation of new components to address those more complex issues. A recent example of this continuing progression is that the CENTURY soil organic matter model was adapted for the DSSAT-CSM modular format in order to better model the dynamics of soil organic nutrient processes. This capability is particularly important to enable CSM to be used for predicting yields in low input cropping systems where soils tend to be deficient in organic matter and nutrients. Organic matter processes are also critical when analyzing the dynamics of cropping systems over long periods of time such as for climate change scenarios. The addition of this more detailed organic matter module provided opportunities to also improve existing components of the model, including energy balance at the soil-plant-atmosphere interface and surface water runoff computations. Conversely, the more detailed organic matter module required additional inputs from existing model components, which were not previously used. Thus, addition of this one new model capability both required and allowed further modifications throughout CSM in order to improve model predictions.