Weeds compete with crops for water, light, and nutrients. However, these parameters are often not individually quantified. This study examined the effect of full sun and shade on corn (Zea mays) and velvetleaf (Abutilon theophrasti) growth and seed production under nonlimiting water and fertility conditions in 2004 at an eastern South Dakota site. Corn density was 6.7 plants/m² and velvetleaf density was 18 plants/m². Shade (40 and 60%) was applied with commercial shade cloth on a wooden frame from the V-3 stage of corn growth until harvest. Corn yield was 141 g/plant in full sun and 61 g/plant in 60% shade. Velvetleaf seed number per plant was 700 in full sun and 440 in 60% shade. In the corn and velvetleaf plots under full sun, velvetleaf averaged 300 seeds/plant,a greater loss than even the 60% shade treatment and implies that corn provided >60% shade to velvetleaf. Corn yield per plant in the mixed plot averaged 92 g/plant which, when estimated using a linear regression for the yield loss data (adj r² = 0.87; p=0.04), suggested that the velvetleaf provided 50% shade to corn. Tissue samples taken at corn VT stage and analyzed for ¹⁵ N indicated corn utilized a higher amount of fertilizer N whereas velvetleaf utilized a greater amount of soil mineralized N.