10 and fig. Rate of growth of the leaves, petioles, and stems closely follows that of the whole plant until the pods and beans begin growth, or at about R4. Shortly after R5.5, dry weight maximizes in these vegetative parts and begins to relocate in the rapidly developing beans. At this time, leaf and petiole loss becomes rapid and continues until R8 when generally all leaves and petioles have fallen, see fig. Root growth begins when the primary root emerges from the planted seed.
Some roots surface.
A portion of the nitrogen used by the soybean plant is made available by fixation of N from the air by Rhizobium japonicum bacteria in the root nodules. These bacteria infect the roots causing nodule production as early as the V1 stage, see fig. Flowering is initiated at R1 on the third to sixth main stem node and progresses upward and downward from there. These first flowers generally appear at the base of a raceme, see fig. By the R5 stage, the plant has completed most of its flowering but a few newly opened flowers may be present on branches and upper main stem nodes.