Field research was conducted in 2000 and 2001 to determine the effect of yellow nutsedge emergence timing and plant density on soybean yield and on yellow nutsedge propagation the following year. Yellow nutsedge tubers were planted at 0-, 7.5- (13/m²), 15- (8.6/m²), 30- (4.3/m²), 60- (2.2/m²), and 90-cm (1.5/m²) in-row spacings with soybean. Yellow nutsedge densities from 2.2 to 13 plants/m² in a high-yield year (2000) and 4.3 to 13 plants/m² in a low-yield year (2001) reduced grain yields 9 to 34%. In a separate experiment, tubers were planted 0, 2, 4, 6, and 8 wk after planting at a 15-cm (8.6/m²) in-row spacing. Seedlings that emerged with the crop and until 2 wk after planting reduced yield 9 to 11%. Yellow nutsedge densities from 1.5 to 13 plants/m² contributed to significant aboveground biomass production, even with a competitive crop, such as soybean. For every gram of aboveground yellow nutsedge biomass produced in the fall, there were more than four shoots present the following spring.

Nomenclature: Yellow nutsedge, Cyperus esculentus L. CYPES; soybean, Glycine max (L.) Merr. ‘Asgrow 3701’