ارزیابی تراکم و ویژگی های رویشی علف های هرز برنج (Oryza sativa L.) در کشت تلفیقی برنج، اردک و آزولا (Azolla sp.)

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In order to evaluate the effects of duck with Azolla sp. on weed density and growth parameters in rice-duck farming system, an experiment was conducted at Sari Agricultural Sciences and Natural Resources University during 2012. Experiment was arranged in split plot based on randomized complete block design with three replicates. Main plots were duck at four levels (control, 400, 800 and 1200 pieces per hectare) and sub plots were Azolla sp. plus reduced amount of nitrogen at four levels (control, nitrogen as the rate of 50 kg ha-1, Azolla as the rate of 500 g m-2 and Azolla plus nitrogen). Weed flora composition in rice field comprised of yellow nutsedge (Cyperus rotundus), small-flowered nutsedge (Cyperus difformis), barnyard grass (Echinochloa cruss-galli), bahia grass (Paspalum notatum), common water-plantain (Alisma plantago aquatica L.) and duckweed (Lemna minor). Results indicated that there were significant differences for effects of duck, Azolla and nitrogen and interaction of these factors in terms of weed density and growth parameters. The minimum amount of small-flowered nutsedge, yellow nutsedge and bahia grass were observed in 1200 duck per hectare plots which treated with Azolla and nitrogen whereas maximum density of those weeds were recorded in rice plots without duck and 50 kg ha-1 of nitrogen (36, 24 and 20 plants m-2, respectively). Results also revealed that 800 and 1200 duck ha-1 in terms of barnyard grass and 400, 800 and 1200 duck ha-1 in terms of common water-plantain and duckweed provided optimal control. In conclusion, it seems that increasing duck number up to 1200 pieces ha-1 along with Azolla and reduced amount of nitrogen is beneficial to control important weeds such as nutsedge and barnyard grass in rice cultivation.