Effect of Flowering Date on Accumulation of Dry Matter and Protein in Soybean Seeds1

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Abstract
The objectives of this study were to determine the effect of time of flowering on the rate of dry matter and protein accumulation in soybean [Glycine max (L.) Merrill] seeds, and to evaluate the relationship between these accumulation rates and the duration of the lag, linear filling, and plateau phases of soybean seed growth.Field studies were conducted on a well‐drained Waukegan silt loam (Typic Hapludoll) at St. Paul, Minn. In 1978 the cvs. ‘McCall’ (Maturity Group 00) and ‘Hodgson 78’ (Group I) were used. In 1979, ‘Altona’ (Group 00) and ‘Steele’ (Group I) were added. On 1 day during both the early and late stages of flowering, 250 flowers were tagged on several plants of each cultivar. During pod filling, pods from these tagged flowers were harvested at weekly intervals for determination of seed dry matter and protein accumulation rates, as well as the duration of the lag, linear filling, and plateau phases of seed growth.We concluded that meaningful relationships between soybean seed growth rate, duration of seed growth phases, and seed size do not exist. However, late maturing seeds of all cultivars consistently had faster (+ 32%) rates of dry matter accumulation, and even faster (+ 42%) rates of protein accumulation in both years of the study. Possible explanations of these fast accumulation rates are discussed.