Evapotranspiration in Crop Simulation Models: Is It Important?.

The overall goal of crop simulation models is to predict growth and development and ultimately final yield and yield components. Although this seems like a relatively easy undertaking, it is a challenging task. In general, a crop simulation model consists of a set of partial differential equations that provide a mathematical representation of the interaction of genetics, environment, and management. These equations encompass scientific information from a broad range of disciplines within agricultural and biological sciences. Given this complexity due to a multitude of interactions, it thus becomes challenging to determine the most limiting factor for conducting a crop simulation scenario. Some state that the genetic factors within a crop model are the most important, while others emphasize the soil surface and profile characteristics. Given that water is a limiting factor in most agricultural production systems across the globe, an accurate simulation of the soil-plant-atmosphere and water balance is critical. Therefore, the prediction of evapotranspiration plays a key role. In this study we explored the importance of evapotranspiration (ET) simulation in the DSSAT suite of crop simulation models. The Cropping System Model (CSM) of DSSAT currently includes two options for the simulation of potential ET. One is the standard Priestley-Taylor equation, while the second one is an implementation of the FAO-56 equation.  The analysis was based on the main crops that are part of DSSAT and for the environments for which the models have been evaluated. Although the correct estimation of ET is important, the methodology we use for the calculation of ET is less important than some of the other factors.