"Kicking the Tires” of the Energy Balance Routine within the Cropgro Crop Growth Models of DSSAT.

Two decades ago a routine called ETPHOT was written to compute evaporation, transpiration, and photosynthesis in the CROPGRO module for grain legumes, such as soybean, of the Cropping System Model (CSM). CSM is the main model of the DSSAT (Decision Support System of Agrotechnology Transfer), which has been widely used to simulate crop production under a wide range of conditions. Although CROPGRO uses daily weather as input, ETPHOT utilizes an internal hourly time step of weather conditions simulated from the daily values. Photosynthesis has been regularly calculated using ETPHOT, but surprisingly, other routines have been used to calculate evaporation and transpiration, even though these data have been available from ETPHOT. Further, ETPHOT computes a complete energy balance, including the simulating the temperature of the crop canopy, yet CROPGRO has “grown” crops at air temperature rather than their own canopy temperature available from ETPHOT. Very often crop canopy temperatures differ significantly from air temperatures, especially for irrigated crops in arid climates. Therefore, improvements in the prediction of crop performance and water use might be made merely by utilizing the heretofore unused and untested energy balance aspects of ETPHOT. This talk describes the results from an effort to “kick the tires” and resurrect this unused but potentially very useful code.