In order to study the effects of summer cover crops and their residues, and mechanical and chemical weed control methods, on weed density and biomass in Valencia orange orchards, an experiment based on randomized complete block design with 7 treatments and 3 replications was conducted in 2005 at Research Garden of Orangery Research Institute of Ramsar, Iran. The treatments consisted of soybean (Glycine max), alfalfa (Medicago sativa), and berseem clover (Trifolium alexandrinum) cover crops,

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... vator, rice straw mulch, glyphosate herbicide, and weedy control. Cover crops were planted on first day of May month as well as rice straw mulch. Rotivator has been done each 30 days until the end of experiment. Herbicide was applied on mid-July month, simultaneously as mowing cover crop. The results of this study showed that soybean and alfalfa cover crops produced the highest and lowest biomass among cover crops, respectively. Similarly, the highest and lowest amount of LAI was observed in soybean and alfalfa, respectively. Soybean cover crop and tillage resulted in lowest weed biomass, while control and alfalfa cover crop resulted in highest weed biomass. Rice straw mulch and berseem clover cover crop have resulted the best in decreasing weed density, while alfalfa cover crop was the most inefficacious one. In conclusion, soybean cover crop and tillage were the most efficacious and alfalfa cover crop was the most inefficacious treatment for controlling weeds in studied orchard.