Evaluation of dense planting adaptation characteristics of small seed soybeans by principal components analysis

For a evaluation method and a selection index for the dense planting adaptation of sprout soybeans, field experiments were conducted with two density levels; dense (30×10 cm, 66 plant m^-2) and standard (60×10 cm, 33 plants m^-2) planting one by using five cultivars of the small seed soybean for sprout, which showing different plant-types for three years. The yield and the number of pods showed a significant positive correlation. Meanwhile, the internode length and the lodging index showed a negative correlation. Characters correlated with the planting density were the internode length, the lodging index, the pods of main stem, and the harvest index as the primary principle components. Other characters like the branch angle, the number of total pods, and the leaf area index were correlated as the secondary principle components. However, the harvest index, the number of pods, and the leaf area were known as influencing factors to both standard and double density. Thus, the internode length, the branch angle, the lodging, and the pods of main stem can be selected as infecting characters to the planting density adaptation.