Abstract
To analyze the influence of early leaf fall during the ripening period of soybean on yield and 100-grain weight, we pruned leaf blades and petioles at 20, 15, and 10 days before maturity (DBM) in 2004, and at 20, 15, and 9 DBM in 2006. The nitrogen contents of the leaves decreased in the order of 20, 15, and 10/9 DBM. In contrast, those of stems, pods, and seeds at maturity decreased in the order of control (no pruning), 10/9, 15, and 20 DBM. Consequently, the total nitrogen content (pruned leaf blades, petioles, stems, pods, seeds) did not change. The yield and number of seeds 5.5-7.3 mm long decreased in the order of 20, 15, 10/9 DBM, and control. In contrast, those of seeds >7.9 mm long increased in that order. The 100-grain weight showed different tendencies between years. Consequently, increasing the loss of nitrogen favored the production of smaller seeds over larger seeds.
