Influence of N Nutrition on Flower and Pod Abortion and Yield of Soybeans

The number of seed produced by a soybean (Glycine max (L.) Merrill) community is one of the important determinants of yield. Since soybeans usually abort a high percentage of their flowers and pods, this study was undertaken to investigate the influence of N nutrition on flower and pod abortion. Experiments in which the N supply to the soybean plant was varied during flowering and pod filling were conducted in the greenhouse and field. The greenhouse experiment was conducted in a hydroponics system with 5 meq NO₃-/liter in the nutrient solution. Some plants were shifted to 12.5 or 18.0 meq NO₃-/liter at initial bloom and maintained at these levels until maturity, while others were exposed to the high NO₃-/levels only until the end of bloom. Treatments in the field consisted of (1) 168 kg N/ha as NH₄NO₃ applied at initial bloom, (2) 168 kg N/ha at the end of bloom, and (3) 168 kg N/ha at both growth stages (total of 336 kg N/ha). The field experiments were conducted on a maury silt loam soil (Typic Paleudalts). Increasing the N supply to the plant during the period from initial bloom to the end of bloom increased yield 33% in the greenhouse and 28 to 32% in the field. Yields were not affected by high levels of N during the filling period. In the greenhouse experiment and one field experiment all of the yield increase resulted from an increase in seed per plant, which was due to an increase in the number of nodes and a reduction in flower and pod abortion. Flower abortion ranged from approximately 55% on the controls to approximately 45% on the treatments giving the maximum yield increase. In a second field experiment, the yield increase came partially from an increase in seed size and partially from an increase in seed number. The data demonstrate the importance of an adequate supply of N to the plant during the period of flowering and pod set for maximum yield.