Aerial dry matter and nutrient accumulation comparisons among five soybean experiments

Efficient and environmentally acceptable nutrient management requires an understanding of when and at what rates nutrients are accumulated by plants. For graminaceous species, a mathematical procedure involving compound cubic polynomials was previously demonstrated to be useful for evaluating growth and nutrient accumulation patterns. Our objective for this study was to compare dry matter and nutrient accumulation rates for determinate and indeterminate soybean [Glycine max L. (Merr.)] by reanalyzing the original data from five field experiments. Data from a maximum yield research (MYR) experiment that yielded 6.8 Mg ha-1 provided information for soybean grown with near-maximum accumulation rates. The high MYR yield resulted from intensive management practices that included high fertilization, high plant population, complete pest control, and timely irrigations to supplement rainfall. The MYR results were compared with rates determined for four non-MYR studies that yielded from 2.2 to 5.4 Mg ha-1 in Iowa, South Carolina, and North Carolina. Contrary to patterns found for corn (Zea mays L.) and wheat (Triticum aestivum L.), no consistent, distinct peaks in accumulation rate were observed for soybean. Instead, trends were masked by short-term variation caused either by responses to environmental variation or by random sampling errors. In addition, computed maximum growth rates for the 6.8 and 5.4 Mg ha-1 studies were higher than the hypothesized maximum rate of 360 kg ha-1 d-1, suggesting either biased sampling or a need to reexamine the theory. These findings lead us to conclude that further research in intraseasonal accumulation patterns for soybean should concentrate on causes for short-term variation, such as weather patterns, via mechanistic simulation. Further, the data for extremely high yields should be considered cautiously until supporting data are found.