Studies on Developmental Morphology and Yield Determining Process in Soybeans : I. Relationship between internode elongation of the main stem and branch develoment

This experiment was undertaken to elucidate branching mechanism in relation to yield determining process of the soybeans, with special reference to phytomer concept. Soybean cv. Tachisuzunari was planted on June 25, 1979. The treatments are three levels of plant population (D1, 3, 333; D2, 1, 667; D3, 833 plants/a) and two levels of nitrogen application (N1, 0 kg N; N 2, 0.3 kg N/a). The experimental design used was 3 × 2 factorial experiment with two replications. The results obtained are summarized as follows: 1. The components of a soybean plant are classified into cotyledon-phytomer, primary leaf-phytomer, phytomer with a compound leaf, prophyll-phytomer and flower cluster-phytomer. These components are arranged in a certain rule. 2. The emerging pattern of successive phytomers on main stem was represented in two linear equations with a turning point at the stage of phytomer 5 emerged. The nitrogen application and plant population effect on the emergence rates before and after the turning point, respectively. 3. There is a co-emerging relationship between main stem and branches. This relationship, however, is not retained under a high plant population such as 3, 333 plants/a. 4. There is a threshold-type relationship between the elongation of internodes on main stem and the number of phytomers developed on predominant branches (II, III, IV), on the basis of co-growing system. This suggests the critical stage of branch development to be on the period of phytomer 5 to 8 emerged, in relation to the distribution of carbohydrates assimilated by the primary leaf and the leaves of phytomer 1 to 3. On the other hand, upper branches such as V, VI and VII do not show this relationship. These branches are relatively stable in the number of phytomers between different plant populations.