As the COMAX/GOSSYM crop simulation and management model has been tested across the cottonbelt, soil hydrology and bulk density data have been needed. Through the course of time over 70 different soil files have been prepared and tested in the model.

A sensitivity test of the model to selected soil physical properties was made. Individual model runs were made where only the soil physical properties were changed, but the weather and all other management practices remained the same.

It has been suggested that perhaps a standard file for each soil textural class could be made instead of individual soil series and textures within a series. The results of these test show that variation in yield predictions, and components of yield such as boll numbers, square numbers, plant height, etc. is as great within a soil textural class as between classes. As an example the variation of yield prediction within the silt loam textural class is as great as the variation from silt loam to clay loam. The reason for this variation is related to the soil water potential and plant water potential calculations. The lower yielding potentials and thus lower plant water potentials and irrigation inputs. This results in either more fruit abortion or less filling of the bolls depending upon demonstrate the need to have individual soil series and soil textures within a series sampled and characterized separately.