This thesis is composed of three manuscripts focusing on the growth and development of soybeans in central Iowa. The first paper in the series focuses on the production of mature seeds and their characteristics. The ability of several soybean cultivars that are adapted to central Iowa to adapt to varying sowing dates is examined. The cultivars chosen for the study cover a range of plant characteristics for Iowa adapted soybeans. The cultivars chosen varied in plant height, leaf size, seed size, and seed oil and protein content. Planting dates spanning 40 days were used to accommodate the range of planting dates used in central Iowa. Yield data for two years indicate plant seed number and yield response to earlier planting are determined by genotype. Oil and protein content of the seed was determined primarily by plant genetics, but early planting decreased protein content and increased oil content. The second paper in the series focuses on how each soybean cultivar achieves the final levels of protein and oil in the mature seed. Each of the cultivars used in the study vary in their capacity to produce oil and protein in their seeds. We found that seed oil concentration is established in the middle of seed development. Seed protein content increased rapidly during seed fill, and continued to increase until seed maturity. The third paper in the series focuses on the ability of current crop modeling software to accurately predict the plant and seed growth characteristics of the cultivars used in this study. Crop modeling is a valuable tool for making agricultural decisions. The model must be robust enough to accommodate the range of soybean genotypes used in central Iowa and their reaction to sowing date variation across years if the model is to be of useful for soybean management. Based upon the model calibration procedure of minimizing RMSE values, calibration of the model for each cultivar and planting date in a growing season is necessary.