INDIANA SOYBEAN SYSTEM MODEL (ISSM) .1. CROP MODEL EVALUATION

A soybean crop model, SOYGRO version 5,41, satisfactorily simulates so ybean growth, development and yield under Indiana conditions, followin g the calibration of varietal coefficients and the use of water retent ion values to approximate soil water limits. Century 84 (MG II) and Wi lliams 82 (MG III) soybeans were grown at two locations during 1985-89 to provide crop growth and yield data for model calibration and valid ation. Model predictions tracked the observed trends in soybean yield over the years, and the patterns of crop growth and development throug h the season. Predicted values of yields, leaf area index and other cr op growth indicators were mostly within one standard error (SE) of obs erved means in 1988 (severe drought) and 1989. Simulation experiments showed that yield potential at Bedford (southern Indiana) was higher t han at Throckmorton (central Indiana) for all planting dates (10 and 2 5 May and 5 June). Century 84 has a slight yield advantage over Willia ms 82 for 10 May planting. If 1988 drought is excluded, this yield adv antages is stochastically dominant. For late planting (5 June), the re verse is true (Williams 82 yielded more). There was no difference for 25 May planting. Using Duncan's multiple range test groupings, a set o f typical weather years were obtained. This grouping, based on crop yi eld potential, will be useful in simulation analysis for pest manageme nt strategy evaluation.