WEED POPULATION INDICES IN IRRIGATED WHEAT FIELDS OF ZANJAN PROVINCE OF IRAN

In order to identify and determine the abundance of weed species in irrigated wheat fields of Zanjan province, Iran, 128 wheat fields in seven counties during 2000 to 2008 were investigated. With counting weed species in each sampling quadrate, population indices were calculated. In each field longitude, latitude and elevation were recorded using GPS (global positioning system). These data were used for producing weed species maps in irrigated wheat fields in Zanjan province. Results showed that 97 weed species were observed within irrigated wheat fields. The most important broadleaved weed species were knotweed (Polygonum aviculare L.), bedstraw (Galium tricornatum Dandy.) and salsify (Tragopogon sp. L.), respectively. Dominant grass weed species were feral rye (Secale cereale L.), blackgrass (Alopecurus mysuroides Huds.), downy brome (Bromus tectorum L.) and bulbous bluegrass (Poa bulbosa L.), respectively. Field bindweed (Convolvulus arvensis L.), common lambsquarters (Chenopodium album L.), hoary cress (Cardaria draba [L.] Desv.) and Canada thistle (Cirsium arvense [L.] Scop.) were the most important disturbing plants prior to harvesting respectively in irrigated wheat fields of Zanjan province. Analysis of weed population based on Shannon-Wiener diversity index showed that the counties were grouped in three clusters. Tarom County was placed in first cluster and had lowest diversity among the counties. Zanjan, Eijrood and Abhar counties had the most species diversity and were placed in second cluster. Mahneshan, Khodabandeh and khorramdarreh were placed in third cluster. Evolution weed population based on Sorensen similarity index showed that, Eijrood with the Abhar had the most composition species similarity, where as Tarom had the lowest similarity with the other counties.