Effect of Row Spacing on Competition of Velvetleaf (Abutilon theophrasti Medic.) with Cotton (Gossypium hirsutum L.)

To investigation the yield and yield component of cotton (Gossypium hirsutum L.) planted in conventional and ultra narrow row spacings, in competition with velvetleaf (Abutilon theophrasti Medic.) an experiment was conducted in a completely randomized block design with split plot arrangement of treatments, with three replications at Experimental Station of Gorgan University of Agricultural Sciences and Natural Resources, during 2011 growing season. The treatments were three row spacings (20, 40 and 80cm) of cotton (as main plot) and five densities (0 (control), 1, 3, 5 and 12 plant.m-2) of velvetleaf (as subplot). Results showed that, almost all vegetative characteristics and yield components of the cotton were decreased with decreasing crop row spacing and increase weed density. In contrast, number of bolls per unit area was increased by reducing cotton row spacing. Rectangular hyperbola model was used to describe relation between cotton yield and weed density. The highest yield (4986.73 kg.ha-1) was obtained in 40 cm cotton row spacing and weed free condition. Cotton yield was decreased with increasing weed density. Based on function estimate, cotton yield lose rooted on come of first weed in competition with cotton planted in 20, 40 and 80 cm row spacing was, 15.59, 34.19 and 66.12, respectively. This study showed that, in ultra-row spacing the cotton is more competitor with over velvetleaf density because increasing the plant density lead to increase the crop ability to resource using in compared with weeds. Too, ultra narrow cotton have produced sustainable yield in competition with over weed density in compared with conventional row.