Soybean Seed Number and Crop Growth Rate during Flowering

Seeds per unit area is an important yield component in soybean [Glycine max (L.) Merrill]; however, the mechanisms regulating seed number are not well understood. Field and greenhouse experiments were conducted to investigate the relationship between photosynthesis during flowering and podset and seeds per square meter. Shade cloth (30 and 63% reduction in insolation) was used to reduce photosynthesis from emergence to Growth Stage R1 in the field ['Pennyrile' (indeterminate) and 'Ripley' (determinate)] or for varying periods during flowering and podset in the greenhouse ('McCall') and field (Pennyrile). Shade during vegetative growth reduced mass per square meter (21‐52%) at Growth Stage R1, but had no effect on crop growth rate (CGR) during flowering and podset (R1 to R5) or seeds per square meter if light interception after R1 was not reduced. Shade during flowering and podset reduced seeds per square meter in relation to the length of the shade treatment. In the field, shade from R1 to R4 and R4 to R6 had similar effects on seeds per square meter; these were less (31%) than the unshaded control for both treatments. These results suggest that maximum photosynthesis throughout flowering and podset may be required to maximize seeds per square meter. There were linear relationships between average CGR during R1 to R5 and seeds per square meter across experiments and treatments in both field and greenhouse. These relationships support previous results suggesting that seeds per square meter is determined primarily by canopy photosynthesis during flowering and podset.