LAUSR

Environmental conditions have a great influence on the growth and development of weeds and, consequently, on their ability to compete, and changing these conditions can be effective in weed management. For this purpose, an experiment was carried out in 2016 and 2017 in the greenhouse of the Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Iran. The studied factors were four weed species Red root pigweed (Amaranthus retroflexus), Jimsonweed (Datura stramonium), Russian knapweed (Acroptilon repens L) and Catchweed (Setaria verticilata) and three irrigation periods to field capacity (irrigation daily (control), irrigation once in every three days and irrigated once every six days). Results showed that with increasing irrigation period, Leaf Area Index (LAI), Relative Growth Rate (RGR), Weed Growth Rate (WGR), Net Assimilation Rate (NAR) and Total Dry Matter (TDM) decreased. The extent of decrease in growth indices was different between weeds C3 and C4. Total dry matter of Catchweed and Red root pigweed responded to increased irrigation periods less than others. In control irrigation, Jimsonweed growth indices were higher than other weeds, but to exert stress and increasing irrigation periods, Red root pigweed was more successful and a stronger competitor.