This monograph is the first effort by the American Society of Agronomy, Crop Science Society of America, and the Soil Science Society of America to publish a book on the use of computer simulation to evaluate agronomic systems. It is a testament to the desire of agronomists to enter a new era of agricultural research and development; a time in which simulation partially substitutes for experiments to determine recommendations for various agrotechnology packages. Improved accuracy in simulating crop and soil systems has convinced a growing number of researchers and technologists of the importance of being able to predict outcomes needed in agricultural decision making. Combining the soil, plant, and climate system into quantitative terms that lead to accurate predictions of outcomes is needed as agronomists enter the information age. The main focus of agronomic research and development efforts in the past few decades has been related to food and feed production. The quality of the environment has now become an imperative issue that crop and soil scientists must address, in addition to maintaining adequate food production. The research needed to find management strategies that optimize high production and minimize environmental degradation will need to include simulation of all or part of the soil-plant atmosphere system. Experimental research alone would require more than an order of magnitude of effort and resources as compared to present levels of production and agricultural activity to adequately reach these goals. An era of low funding for agricultural research and extension makes the use of simulation models even more of a necessity as a major assistance tool for helping with decision making in sustainable agricultural systems. Progress made by using models is much faster and less expensive than throug experimental research alone. Key simulated results, however, must continue to be evaluated with field experiments. The chapters in this monograph have been written to provide examples of models of component processes necessary to simulate the dynamics of crop and soil systems. The information is intended to be useful to researchers, extension and other professional technologists, and teachers. For researchers, the models of processes will define details regarding information necessary from experimental trials to adequately simulate results of those experiments. Because every step in a simulation must be clearly defined, the lack of accuracy in simulating various processes also helps to identify gaps where additional research is needed. For professional agronomists who recommend technological packages to farmers and other users of crop and soil information, models could provide reasonable and quick answers to the "what if " questions for specific soil, and management combinations. For teachers, the use of computer simulation models can ....
