Full-season Palmer amaranth (Amaranthus palmeri) interference with cotton (Gossypium hirsutum)

Four field experiments were conducted in Oklahoma to measure full-season Pa lmer amaranth interference on cotton lint yield and fiber properties. Densi ty of the weed ranged from 0 to 12 plants 10 m(-1) of row. Cotton lint yiel d vs. weed density fit a linear model for densities less than or equal to 8 weeds row(-1) at Perkins and Chickasha in 1996 and at Altus in 1997. At Pe rkins in 1997, all densities fit a linear model. For each increase of 1 wee d row(-1), lint yield reductions were 62 kg ha(-1) (or 10.7%) and 58 kg ha( -1) (or 11.5%) at Perkins and at Chickasha in 1996, respectively. At Perkin s and Altus in 1997, for each 1 weed row(-1), lint yield was reduced 71 kg ha(-1) (or 5.9%) and 112 kg ha(-1) (or 8.7%), respectively. Lint yield vs. end-of-season weed volume fit a linear model except at Altus in 1997. For e ach increase of 1 m(3) of weed plot(-1), cotton lint yield in 1996 was redu ced by 1.6 and 1.5% at Perkins and Chickasha, respectively. In 1997 at Perk ins and Altus (less than or equal to 6 weeds), each increase of 1 m(3) of w eed plot(-1) reduced lint yield 1.6 and 2.3%, respectively. Lint yield vs. end-of-season weed biomass fit a linear model in all four experiments. Lint yield was reduced 5.2 to 9.3% for each increase of 1 kg of weed biomass pl ot(-1). Fiber analyses revealed significant differences for micronaire (fib er fineness) among weed densities in two experiments, marginal significance in a third, and none in a fourth. An intermediate number of weeds often re sulted in improved fiber micronaires in these environments. No other fiber properties were influenced by weed density.