Evaluation of Some Ecophisiological Aspects of Pondweed (Potamogeton nodosus Poir.) in Response to Fertilizers Levels, Rice Variety and Flooding

Pondweed tolerance to flooding and most herbicides, as well as regrowth after hand weeding, has led the weed to be considered as an invasive species in paddy rice. Three experiments were carried out to provide a strategy for management of pondweed. In the first experiment, the interference of pondweed with Hashemi and Gohar rice cultivars at 0, 50, 100 and 150% of recommended NPK fertilizer were studied. In the second experiment, pondweed proliferation and colonization at the above fertilizer levels; and in the third experiment, the effect of water depth on the growth of this weed were investigated. The result of the first experiment showed that pondweed does not have significant effect on the yield of Gohar cultivar, but decreased the yield of Hashemi by 13-25%. Decreasing the fertilizer level to 50 and zero percent of recommended doses led to sharp decline in the performance of both rice cultivars in competition with pondweed. According to the results of the second experiment, the pondweed colony expansion in the 50% recommended dose of fertilizer treatment was twice that of 100% fertilizer treatment. The result of third experiment showed that, increasing the water depth to 7 and 14 cm led to 359 and 342 percent increase in pondweed shoot biomass in comparison to saturated treatment. In general, according to the results of this research, the reason for the outbreak and damage of pondweed can be attributed to the nutritional weakness and the deep and long flooding of the paddy fields. In case of efficient use of fertilizers, drainage and the use of appropriate cultivars, it is not necessary to spend a lot on frequent hand weeding and the presence of weed will not cause significant economic losses of rice.