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equations and days were integers in the model; dry weight can increase from 0.0 g to 0.03 g or higher in one day. Linear extrapolation to zero was performed on the four days previous to measurable dry-weight appearance (and disappearance) to smooth out the curve. The adjustment did not affect the performance of the model; the model-derived curves more closely represented the biology of the system. The model was set to run 123 days from planting. The time duration was set by the equation describing the leaf dry-weight accumulation; the soybean fields under intensive study for two consecutive seasons were harvested 123 and 124 days after sowing.
The correlation coefficients and the coefficients of determination were not 1.00 for any of the regression equations. The field data may be biased, which would produce a less-than-perfect fit. The field data may not be accurate or may not accurately represent the actual plants, again introducing bias. Random variation, a
common obstacle with field data, likely accounts for most of the variation. Had the correlation coefficients been less than 0.80 or the coefficients of determination less than 0.60, some concern as to whether- the regression equations accurately described the field data might be warranted. The data were well fitted by the
presented equations (Figures 1 7).