Investigation on the effect of different wheat based crop rotations on weed seed bank of wheat fields in Miyaneh region

Effect of wheat based crop rotations including wheat and corn, wheat and sunshade, wheat and onion and wheat and sorghum rotations on weed seed bank of wheat farms was investigated in around of research field of Islamic Azad university, Miyaneh branch. Soil samples were collected at 0-0 and 0-0 centimeter soil depth using Uger in September 005. Experiment was carried out with five treatments as factorial in a completely randomized design with 5 replications and continuous cultivation of wheat was considered as control. Leaching with cloth bags method was used to study of seed weed bank in different treatments. In this research, 44 weed seeds belonging to 5 species were collected and identified. The results of variance analysis revealed that Cyperus fuscus L. seeds in control and wheat and corn treatments, and Amaranthus retroflexus in wheat and sunshade, wheat and onion and wheat and sorghum rotations were more frequent. Seeds of A. blitoides, A. retroflexus, Avena fatua L., Fumaria spp. and Cuscuta spp. were also seen in all treatments. However A. retroflexus, C. fuscus, A.blitoides and Fumaria spp. were the most frequent of common weeds of wheat farms, respectively. Seed production of Fumaria spp., Setaria verticillata, Schoenoplectus mucronatus L., C. fuscus, Hibiscus trionum L. and Portulaca oleracea L., in all rotation treatments was much less than control. However the mentioned treatments had not significant effect on seed numbers of some weeds such as A. blitoides, C. fuscus, Sorghum halopens and P. oleracea. In continuous cultivation of wheat (control), seeds of two mentioned Amaranthus species, S. halopens, Polygonum hyracanicum, P. paulum, S. verticillata, Hyosyamus spp. and Marribium vulgare L. were significantly less than those of wheat and sunshade treatment. Also seeds of Euphorbia spp., Cuscuta spp. and P. paulum, in comparison to wheat and onion, Sisymbrium loesselii L., in comparison to wheat and corn and Aleopecurus myosuroides Hudson, in comparison to wheat and sorghum treatments were significantly more than control. In the other word, some weeds were better controlled by continuous cultivation of wheat. Rotations of wheat and sorghum, wheat and onion and wheat and corn caused significant reduction in seed bank of 5 collected weed species. However, total numbers of collected weed seeds at two studied soil depths had no significant differences.