Ecological Effects of Barnyardgrass on Soybeans in a Greenhouse

Greenhouse studies were conducted to study the competition between soybeans [Glycine max(L.) Merr. ‘Vansoy’] and barnyardgrass [Echinochloa crus-galli(L.) Beauv.]. The competition was initiated or terminated when soybeans were 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks old. The reproductive efficiency of soybeans was not lowered by 4 to 7 weeks of competition after planting of soybeans. Competition between the two species for the entire growing season resulted in a significant decrease in plant height of soybeans. The total dry matter per plant was negatively correlated with an increase in the length of competition. Competition during the first 5 to 9 weeks of the life cycle of soybeans was more deleterious to soybean productivity than the last 5 to 9 weeks of its life cycle.