Effect of row spacing in competition of cotton with velvetleaf on crop growth

To evaluate the competition effect of velvetleaf on cotton، 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 spacing (20، 40 and 80cm) of cotton (as main plot) and five densities (0 (control)، 1، 3، 5 and 12 plant per m-2) of velvetleaf (as subplot). The highest cotton height (129. 4 cm) was obtained in 80 cm cotton row spacing and weed free condition. Also، maximum cotton dry matter (863. 8 g m-2) and leaf area index (9. 04) was achieved in the plot of 20cm cotton row spacing and weed free condition. Results indicated that row spacing had no significant effect on cotton yield under weed free condition. The highest yield (4986. 73 kg ha-1) was obtained in 40 cm cotton row spacing and weed free condition. However، results showed that in ultra narrow row، increasing the plant density lead to increase of the crop ability to resource using in compared with weed and have produced sustainable yield in competition with over weed density in compared with conventional row.