Effect of Environmental and Management Factors on the Weed Species Richness of Summer Crops in Ilam Province

This study was performed in order to assess the weed species richness in summer crop fields. 21 fields were chosen in Sarableh, Darrehshahr and Dehloran, Ilam province with different climatic patterns during 2009-2010. Their demographic indices were calculated. The geographic information was recorded by GPS for each field. Results showed that 26 weed species can be found in corn fields (main summer crop) of Ilam province. According to abundance index, the most common broad leaf weeds in corn fields were Heliotropium europaeum L., Amaranthus bliotoides L., Convolvulus arvensis L. and Hibiscus trionum L. The dominant grass weeds were Sorghum halpense L. and Echinochloa crus galli L. The highest stability index (77.77 %) was related to S. halpense and A. bliotoides in corn fields. Therefore, they are the most persistent weeds in these fields. All environmental factors such as climatic condition, and elevation affected weed species richness and structure. The greatest effect on weed species richness was related to crop type and sowing date.