Analysis of root growth characteristics based on a pipe-model theory and distribution of root nodules in soybean (Glycine max Merr.)

Based on the pipe-model theory, the root growth characteristics and root no dule distribution in soybean grown in pots were analyzed, using the variety Fukuyutaka and two mutants derived from the variety Enrei, super-nodulatin g (En6500) and non-nodulating. Fukuyutaka plants were grown under various n itrogen levels, soil hardness, shading levels and bacillus densities, in so il. The ratio of the amount of thin roots which does not conform to the pip e model to that of thick roots which conformed to the model was nearly the same regardless of cultivation conditions. The formation of nodules began i n minute radicles of 0.2-0.3 mm diameter class, and about 95% of root nodul es were distributed in the thin roots of 1 mm or less. a high correlation w as observed between the amount of roots and the number of root nodules in e very root-diameter class. However, the big root nodules (larger than 3 mm i n diameter) tended to be distributed over all root-diameter classes equally . It was suggested that the distribution of the root nodules with high nitr ogen-fixing ability is closely related to the amount of the vascular bundle s in each root diameter class.