Two-dimensional infiltration and soil water redistribution models were developed for use with the GOSSYM cotton crop simulation model. The new soil water process models were developed independently and tested with a stand-alone soil solution movement model, which facilitated testing of specific model attributes. Flexible structure and boundary conditions in the models work within the framework of the current GOSSYM release and allow for future developments planned for the GOSSYM/COMAX software.

The infiltration model allows for use of soil permeability (infiltration capacity), where such data are available, or application of the Soil Conservation Service runoff curve number method to estimate runoff depth and net infiltration of water applied to the field. A mixed-form Richards equation, which uses both energy gradient and mass balance to simulate fluid flow, is used to accomplish water flow within the soil profile. A simple two-dimensional finite difference numerical solution technique facilitates simultaneous vertical and horizontal water movement approximations. Hourly time steps are built into the infiltration and redistribution models, and permit the use of hourly or daily weather station precipitation data. The design of the models developed through this work includes flexibility sufficient to facilitate alternative cropping and irrigation systems.

The new soil water movement models were incorporated into GOSSYM, and the resulting modified GOSSYM was tested under a number of different scenarios. Performance of the models under the testing conditions was satisfactory, although the solution time was increased somewhat over the current GOSSYM release. Further verification of the model will be pursued, as appropriate field and/or laboratory data are obtained.

Improved model solution techniques, energy-driven water flow simulations, and flexible boundary conditions incorporated into the new soil water models are the major contributions of this work. Use of these models should extend the applicability of GOSSYM, by accommodating a greater range of soil conditions and more diverse cultural practices.