Rate of Dry Matter Accumulation in Soybean Seeds with Varying Source‐Sink Ratios1

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Abstract
The rate of accumulation of dry weight in the seed is one important process in yield production by grain crops. Information on factors influencing the seed growth rate are needed to help identify yield limiting processes. This study was undertaken to determine the effect of varying source‐sink ratios on the rate of dry matter accumulation in seed of soybeans (Glycine max (L.) Merr.). The varying source‐sink ratios were obtained by removing approximately 50% of the pods or 66% of the leaf area (two leaflets from each trifoliolate leaf) at the end of the flowering period. The study was conducted for 2 years in the field.The pod removal treatment reduced pod number by 20% at maturity and resulted in an increase in weight/seed over the control near the end of the filling period in one of the years. Removal of two‐thirds of the leaf area reduced the weight per seed near the end of the filling period in both years of study. Pod weights of the pod removal treatments were generally heavier than the control and the pods from the leaf removal treatments were lighter than the control. Defoliation lowered the concentration of sugar in the stem sap compared with the control; but, pod removal increased the concentration of stem sugars only near the end of the filling period. The data are interpreted as suggesting that seed growth rates are not closely related to photosynthate production and that storage carbohydrates serve as a buffer between seed growth and photosynthate production.

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