An experiment in growing soybean was conducted at the Czesławice Experimental Farm, belonging to the University of Life Sciences in Lublin, over the period 2018–2020. Three experimental factors were included in this study: cultivation method (conventional and organic), soybean cultivar (Aldana and Merlin), and row spacing (22.5 cm and 35 cm). The species composition, number, and air-dry weight of weeds were evaluated. The Shannon-Wiener diversity index (H’) and the Simpson dominance index (SI) were also calculated for the weed community in the soybean crop. Compared to conventional farming, organic cultivation significantly increased the number and dry weight of weeds as well as the numbers of the dominant species Echinochloa crus-galli. A significantly higher number and dry weight of weeds were found in the cv. Aldana crop than in the case of Merlin. In comparison with narrow-row cultivation, sowing soybean at the wider row spacing resulted in a greater number of weeds, in particular of the species Echinochloa crus-galli. Interrow width in the soybean crop did not cause differences in weed dry weight. The experimental factors slightly modified the Shannon-Wiener (H’) and Simpson (SI) indices.