effects of crop rotation on weed density, biomass and yield of wheat (titicum aestivum l.)

in order to study the weed populations in wheat, under different crop rotations an experiment was carried out at agricultural research station of jolgeh rokh, iran. during growing season this project was done in five years, based on randomized complete bloch design with three replications, on crop rotations included: wheat monoculture for the whole period (wwwww), wheat- wheat- wheat- canola- wheat (wwwcw), wheat- sugar beet- wheat-sugar beet- wheat (wswsw), wheat- potato- wheat- potato- wheat (wpwpw), wheat- potato- wheat- canola- wheat (wpwcw), wheat- sugar beet- wheat- potato- wheat (wswpw), wheat- maize- wheat- potato- wheat (wmwpw), wheat- maize- wheat- sugar beet- wheat (wmwsw). data analysis was done in fifth year. weed sampling was done at four growth stages of wheat, including tillering, shooting, heading and soft dough stage of grains. density, dry and fresh weight of each weed species per unit area, besides wheat grain yield were determined. all analysis of variances for traits related to weed were statistically significant (p≤0.01). the highest weed biomass was obtained in heading stage of wheat, and the greatest weed dry matter in all four growth stages was achieved in wwwww rotation and the least one in wmwsw rotation. the highest weed density in different growth stages was achieved in rotations 7, 3, and 6. wheat grain yield in all crop rotation treatments had a significant increase compared to monoculture. it seems that, yield reduction of wheat monoculture is related to weed density, its population and higher weed biomass in this treatment.