In order to study the different levels of irrigation on diversity, density and compound of weed species in corn field, experiment was conducted at Ferdowsi University of Mashhad Research Field (360 15\\\\\\\\\\\\\\\"1atitude, 590 28\\\\\\\\\\\\\\\" longitude and 985 m elevation). The experiment was based on interval mapping with four levels of irrigation (6130, 7290, 8800 and 12330 .m-3 ) and four levels of weed control (complete control, broad-leaves control, grasses control and without control). Weed sampling was done at 4 stages including first, meddle and end of critical period weed control and harvest then all species counted species separate. The results showed that in different levels of irrigation the weed species were different. At the first time of critical period, the most diversity was in 8800 and 7290 m·3 and the minimum diversity was in 12330 and 6130 m -J irrigation levels. At the harvest time, the most diversity was in 12330 and 6130 and 8800 m·3 irrigation levels respectively and least diversity within different indexes were in 7290, 8800 and 6130 m·3 irrigation levels respectively. Stability index changed at different levels of irrigation. In addition, Maximum when the irrigation level was in minimum level, however, highest level of irrigation caused the maximum Unstability of species but levels of irrigation had no significant on dominance Index.

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