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measurements were comparisons against leaf-area diagrams and insect- and disease-rating scales developed for soybeans (Appendix E). On each sampling date, the above-ground plant was separated into stems, leaves, petioles, pods, and seeds. The plant parts were dried and weighed. The relationship between leaf area and
leaf dry weight was determined from these plants. A separate regression equation was developed for each dependent variable; time was used as the quantitative independent variable, with up to 15 degrees of freedom available for the regression equation.
The equation which described the leaf dry-matter accumulation over time was used to drive the model. The separate regression equations which described dry-matter accumulation by pods, stems, seeds, and petioles at each day, were related mathematically to the equation which described dry-matter accumulation by leaves alone. The relationship was strictly a ratio. The ratios of stems : leaves, seeds : leaves, pods : leaves, and petioles : leaves were established for each day of the model. The equation which described leaf dry-matter accumulation over time produced stems, seeds, pods, and petioles, varying in dry-matter accumulation proportional to leaf dry-matter accumulation. Problems associated with mathematical descriptions of biological data were handled as they arose. Dry matter of the plant organs