SIMULATION-MODELS - SCIENCE, SNAKE OIL, EDUCATION, OR ENGINEERING

Crop simulation models can be divided into two groups: those that aspi re to improve our understanding of the physiology and environmental in teractions of crops (science), and those that aspire to provide sound management advice to farmers of sound predictions to policy makers (en gineering). These quite different aspirations require quite different models. Scientific models rue mechanistic. With a few exceptions, they have failed to meet their aspirations, They are typically flawed by b eing based on untestable guesses about the processes that control grow th. They may, however, provide useful self-education for their develop ers. The best engineering models me based on robust empirical relation s between plant behavior and the main environmental variables. Because of their empirical nature, we should not expect them to apply outside the range of the environmental variables used in their calibration. W ithin their calibrated ranges, however, some have proved useful in pro viding sound management advice. It is hard to see a useful role, other than self-education, for models that Tan between the scientific and t he engineering types.