effects of crop rotation in combination with chemical control on weeds density and their interactions, in golestan province wheat fields

in order to study crop rotation, chemical control and their interactions on weeds density of wheat fields, an experiment was conducted in a split plot arrangement in randomized complete block design with three replications in gorgan agricultural research station for five years. in this study, 10 rotational crops: canola, fababean, barley, white pea, soybean, cotton, maize, sorghum, millet and wheat were assigned to main plots and using herbicides and no weed control were randomized in sub plots. herbicides were selected in way to have minimum residual effects on next planting crops. weeds flora and their density were recorded one month before harvesting time. results showed that crop rotation decreased spring weeds (up to 36%). crop rotation also decreased autumn weeds significantly, if corn was considered as summer cultivation. results also indicated that wheat-maize rotation can reduced weeds density up to 33% more than rotational systems where maize is cultivated once every five years. during the period of five years, weed populations was not controlled by chemical method singly. effective effect was observed in chemical method, when summer plants such as soybean, cotton, and maize be considered in rotational system.