Influence of Day and Night Temperature on Soybean Seed Yield

Growth temperature influences the seed yield of soybean Glycinemax (L.) Merr.. Most studies have concentrated on the effects of concomitant increases in day/night temperature during the entire life cycle of soybean. A better understanding of the influence of combinations of high day and night temperature imposed during different reproductive growth phases on soybean seed yield would be beneficial in identifying yield limiting factors. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30°C were imposed during flowering and pod set (R1‐R5), seed fill and maturation (R5‐R8), and during the entire reproductive period (R1‐R8). Increases in day temperature resulted in decreased seed formation when plants were exposed during flowering and pod set and decreased seed growth when exposed during flowering and pod set or seed fill. Seed growth reductions in plants exposed to the high day temperature were accompanied by decreased photosynthetic rates. The largest yield reduction in this study was 27% and occurred when 35°C occurred for 10 h per day from flowering to maturity. No significant losses in yield occurred at high night temperature at any reproductive growth phase. The only significant interaction between day and night temperature for the yield components was for seed weight per plant during flowering and pod set. Night temperature stress did not occur at 30°C and a night temperature of 20°C did not reduce the yield loss from daytime high temperature stress. This study suggests that soybean seed yield reductions from high temperatures are primarily a response to day temperature and moderate to high night temperatures have a small affect on soybean seed yield components.