The objective of this study was to compare the competitive abilities of soybean plants with those of competitor genotypes through the design of replacement series. There were performed six experiments at UFRGS, in Porto Alegre - RS, in 2001 and 2002. The treatments tested were five proportions of plants among soybean and competitor genotypes: 100:0; 75:25; 50:50; 25:75; and 0:100. Soybean was represented by the cultivars 'IAS 5' and 'Fepagro RS 10', and the competitors by forage radish or by the soybean cultivar 'Fundacep 33'. The treatments were arranged in a completely random experimental design, with four replications. The competitivity analysis was accomplished through diagrams applicable to the substitutive design and interpretation of competitive indexes. It was proved that the proportion among soybean plants and forage radish plants changed the competition relation among these species, but that the proportion among soybean plants from different cultivars did not altered such relationship. Radish was more competitive than the soybean cultivars 'IAS 5' and 'Fepagro RS 10', whereas the competitivity of 'Fundacep 33' genotype was equivalent to these cultivars.
competitivity; substitutive design; Raphanus sativus