فهرست مطالب مجتبی ولایتی

In order to evaluate the effect of cotton (Gossypium hirsutum) and common lambsquarters (Chenopodium album) densities on yield and yield components of cotton, a field experiment was conducted in the Agricultural Research station in Birjand University, Iran. A factorial experiment was carried out in a complete block design with three replications. Treatments included weed density (0, 6, 9, 12 plants.m-2) and crop density (6, 9, 12 plants.m-2). Three pure stand of common lambsquarter densities (6, 9, 12 plants.m-2) was added to each block. Results indicated that there was a significant decrease in yield and yield components of cotton under weed densities. Six plants.m-2 of weed caused 15% decrease in seed cotton and increase of weed density up to 9 and 12 plants/m2 caused further decrease in seed cotton. These weed densities (6, 9 and 12 plants.m-2) caused 16, 30 and 45% decrease in cotton seeds respectively. Lint yield was decreased 13, 24 and 42% as weed density increased from 6 plants.m-2 to 9 and 12 respectively. In this experiment, increasing cotton density was able to soften the negative impact of increasing weed density. Increasing crop density can be utilized effectively to minimize cotton yield reduction due to weed interference.

Most allelopathic studies have demonstrated the importance of live and dead plant tissues as source of allelochemicals. Seeds of several species also have inhibitory effects on germination of the same or other species. In order to determine the allelopathic effects of common lambsquarters (Chenopodium album) seeds, an experiment was conducted under controlled conditions in Birjand University, IRAN. The laboratory experiments were carried out in a completely randomized block design with 6 replications. Four treatments of each crop species were consisted of 15 seeds of shattercane (Sorghum bicolor) and/or 10 seeds of maize (Zea mays) with 0, 200, 400 and 600 seeds of common lambsquarters that were equally distributed around seeds of both crop species. Results indicated as the number of weed seeds increased, the crop germination percentage was decreased significantly. There were significant effects of neighboring weed seeds on coleoptile and radicle length, number of secondary and adventitious roots and length of secondary and adventitious roots of crop species.

Weeds are problematic plants in agroecosystems as a competitor for crops. In order to evaluate effects of cotton (Gossypium hirsutum) and common lambsquarter (Chenopodium album) densities on some crop growth indices, a study was conducted during 2006 in Experimental Station of Faculty of Agriculture, The University of Birjand as factorial experiment based on complete randomized block design with four replications. Three densities of cotton (6, 9 and 12 Pl.m-2) and four weed densities (0, 6, 9 and 12 Pl.m-2) were used to provide different weed interference levels. Indeed, three plots in each replication were intended to cultivation of lambsquarter alone at 6, 9 or 12 Pl.m-2. Results showed that crop growth rate (CGR) of cotton was influenced by weed density, and its relative growth rate (RGR) and net assimilation rate (NAR) indicated a declining trend as weed density increased. Dry matter accumulation of cotton also was affected negatively by weed densities, as interference of lambsquarter at 6, 9 and 12 Pl.m-2 resulted to 35, 42 and 48 percent dry matter reduction, respectively, than weed-free treatment. Increasing of cotton density could partly compensate for negative impact of weed attendance on cotton growth. Thus, it seems higher plant densities can be used as a managing tool against weeds in cotton fields to avoid reduction of yield.