Field experiments were conducted in 1992 and 1993 to determine the eff
ect of N fertility, cropping system, redroot pigweed (Amaranthus retro
flexus L.) density, and harvesting frequency on collard (Brassica oler
acea var, acephala D.C) and cowpea [Vigna unguiculata (L.) Walp.] grow
th. The N fertilization regimes were 0, 80, 160, and 240 kg.ha(-1), ap
plied as urea in a split application, Four weeks after crop planting,
redroot pigweed was seeded at 0, 300, and 1200 seeds/m(2). Between wee
ks 6 and 12, collard leaves were harvested at 1- to 3-week intervals,
Year, N fertility, and cropping system interacted to determine collard
leaf number and mass. For example, in 1992, with N at 160 kg.ha(-1),
collards intercropped had more total leaf mass than those monocropped,
Pigweed density had no effect on collard yields, which were greatest
from the 3-week harvest frequency. Cropping system and pigweed density
interacted to determine cowpea vine length, shoot dry mass, and branc
hing. The high density of pigweed caused a 56% reduction of coupes dry
mass in 1992.