The GOSSYM/COMAX crop management system consists of a materials balance cotton model and an expert system that uses the model for crop management decision making. The COMAX expert system embodies knowledge that enables growers to use the predictive capability of GOSSYM to assist in making crop management decisions. A redesign of COMAX has been undertaken to improve the flexibility of the expert system and to increase its knowledge content. In the 1991 release, COMAX has been implemented as a multi-dimensional tool that allows the user to select one or more advisory options.

One difficulty with the old version of COMAX was its inflexibility with respect to the wide variety of management practices encountered across the cotton belt. We considered two alternatives in addressing this problem. One was the incorporation of regional rules for different parts of the cotton belt and the other was the implementation of user-specified rules. Although the use of regional rules would allow the system to make more specific recommendations, this alternative was rejected for the following reasons: 1) the number of regions would necessarily be quite large, 2) there are a wide variety of management practices within each region, and 3) the incorporation of these specific sets of regional rules would limit the user's ability to analyze "what-if" scenarios with the system. User-specified rules, on the other hand, allow the recommendations to be tailored to each grower's crop management practices and gives the user "game-playing" capability.

User-specified rules have been incorporated in the irrigation, fertility, PIX, and crop termination components of the system. In the irrigation component, user-specified rules allow the user to decide when to start considering the need for irrigation and when to terminate consideration of irrigation. These start and stop points can be specified as calendar dates or with reference to markers, i.e. start a certain number of days after emergence, or stop at a specified percentage open bolls. In the fertility advisor, user-specified rules allow the user to apportion fertilizer applications throughout the season in the percentage he would like to consider using, and to specify the method and type of fertilizer to be applied at different parts of the season. PIX applications can be scheduled to begin relative to phenological markers such as matchhead square or first bloom. In the Crop Termination option, the relative timing of PREP and defoliants is determined by a user-specified rule.

In conclusion, user-specified rules allow the grower to tailor the behavior of the expert system to his crop management practices while still providing enough flexibility for evaluation of alternative management practices. The new design of COMAX will allow the incorporation of more of these rules as new capabilities are added to the system.