How Much of Soybean Yield is Derived from Remobilized Dry Matter?.

Previous reports have confirmed that final soybean yield [Glycine max (L.) Merr.] is partly determined from remobilization of dry matter (carbohydrates and protein) from leaves to the seed during the final stages of the seed filling period (SFP).  However, few studies have quantified the role of remobilized dry matter on yield.  The objective of this study was to determine the percentage of final yield derived from remobilized dry matter during the last ½  SFP.  Data were collected from five previous growth dynamic studies that involved a wide range of cultural and environmental factors conducted near Baton Rouge, LA (30^o N Lat) across a 9-year period (1987-1995).  Seed dry matter (SDM) from remobilized dry matter was calculated as follows:

1.  From dry matter samples taken at regular intervals during SFP, the percentage of final yield accrued during the last ½ SFP was determined.

2.  The percentage determined in step 1 was multiplied by yield (plot yield converted to dry matter and multiplied by 2 to correct for energy cost) to obtain SDM accrued during the last ½ SFP.

3.  SDM accumulated by  crop growth rate (CGR) (corrected for leaf and petiole abscission, and the energy cost of seed production) during the last 1/2 SFP was determined.

4.  Percentage of yield due to  remobilization was calculated as follows:

[[(SDM last ½ SFP)- (SDM  from CGR last ½ SFP)]/ [Total SDM as determined from plot yield]] X 100

Results indicated that in almost all cases, CGR during the last ½ of SFP was not sufficient to account for SDM accumulated during this period; and that  remobilization was responsible for about 10-20% of final yield.  In conclusion, remobilized dry matter makes a significant contribution to yield formation during the last ½ SFP.