RICE WEED COMMUNITY COMPOSITION AND RICHNESS IN NORTHERN IRAN: A TEMPERATE RAINY AREA

Knowledge about weed density and composition plays an important role in weed management decision making.Surveys were carried out to study the weed flora composition in rice fields of Guilan Province in Iran.481 fields from 16 regions were selected for survey.Weed samples were taken with a W-shaped sampling pattern.Weed species were identified and the plant density, percentage frequency, uniformity, and abundance indices were determined.Biodiversity was calculated using Shannon-Weiner (H′) and Simpson (D) diversity indices.A total of 66 species, belonging to 43 genera and 29 families were identified.The highest number of weeds belonged to the two families Cyperaceae and Poaceae with 15 and 8 species, respectively.The most frequent weed species were Echinochloa crus-galli (89.8%), and Paspalum distichum (79.4%),Echinochloa oryzoides (60.3%),Cyperus difformis (56.5%),Ecliptal prostrate (49.5%),Cyperus serotinus (34.7%),Azolla filiculoides (34.5%),Sagittaria trifolia (31.6%),Cyperus esculentus (31.6%) and Alisma plantago-aquatica (28.7%).Relative abundance index indicated that the annual weed species were more dominant than the perennial ones.Based on Shannon-Weiner and Simpson's diversity indices Talesh area had the highest weed diversity (H′ = 2.85; D = 0.916) and Rudbar showed the lowest diversity values (H′ = 1.97;D = 0.749).