the effect of duck’s presence (anas platyrhynchos) in the rice fields on rice yield (oryza sativa l.) and yield components. and its effects on weed density

in order to indicate the effect of duck's presence, anas platyrhynchos in paddy fields on rice (oryza sativa l.) yield, yield components and its effect on weed density, an experiment was carried out in baz ghaleh dezh village, located in sangar, guilan, iran in 2013. this experiment was performed based on factorial split-plot analysis conducted in a randomized complete block design (rcbd). each treatment was applied in three replications. in this experiment the main factor (duck) had two levels (in the presence of duck and in the absence of duck) and the minor factor was the factorial combination of weeding levels (weeding on the releasing day of ducks and not weeding on the releasing day of ducks) and also the planting spaces were 20×20, 25×25, 30×30 cm. the results of variance analysis of rice data showed that duck's presence on paddy field causes 17.28% filled grain per panicle, 6.19% one thousand grain weight, 11.13% harvest index (hi), and 9.5% grain yield. also, the results of variance analysis of weeds data showed that duck's presence on paddy field can make a significant effect on number and biomass of weeds echinochloa crus-galli, scirpus  maritimus, paspalum distichum, and weeds density at harvest time. the results showed that duck's presence causes reduction of 38.93% of echinochloa crus-galli, 58.29% of scirpus maritimus, 47.48% of paspalum distichum at the harvest time, 34.58% of biomass echinochloa crus-galli, 40.88% of scirpus maritimus biomass, 62.69% of paspalum distichum biomass, and 53.77% of weeds at the harvest time in comparison with treatment by duck's absence on paddy fields.