Survey of weeds species diversity and community structure in irrigated wheat fields of Aibak Abad region of Arak city

In order to identify and determine the plant density, species diversity and abundance of weeds in wheat fields of Aibak Abad region in Arak city of Iran, 50 farms in 2013 was investigated in a field study. Fields based on their area in the ranges of Less than 1 hectare, 1 to 2 hectares, 2 to 4 hectares, 4 to 8 hectares, 8 to 16 hectares were identified. According to the area of farms, randomize sampling based on w pattern was performed using 0.5 on 1 square meter quaderates. 64 weed species from 23 plant families were identified. Poaceae and Brassicaceae families with 17 percent of relative importance were the most important families. according tothe results the dominant weeds in wheat fields of Aibak Abad Based on importance were Corn flower (Centaurea depressa), Tansy mustard (Descurainia Sophia) Binweed (Convolvulus arvensis L.) Foxtail grass (Alopecurus myosuroides), Cone catchfly (Silen conidia), Cow cockle (Vaccaria pyramidata), Plumeless Thistle (Carduus pycnocephalus) and (Cardaria draba). The results showed that by increasing the area of fields, the weed plant density, weed species diversity such as Shannon-Wiener diversity index and Simpson index decreased. Analaising of questionnaires filled in by farmers showed that fieldes management approaches especially herbicide application are known as the main reason of changes in the weed species composition of irrigated wheat field of Aibak Abad.