Competitive interactions between weedy rice and cultivated rice as a function of added nitrogen and the level of competition

The competitive outcomes between weedy rice from Malaysia (MWR), the Philippines (PWR), and Vietnam (VWR) and cultivated rice (IR64) grown in pots were evaluated in a replacement series experiment with added N (0, 50, 100, and 150 kg N ha^?1) and competition with IR64 plants (no competition, eight weedy rice plants : 0 IR64 plants; low competition, six weedy rice plants : two IR64 plants; and high competition, two weedy rice plants : six IR64 plants). The growth observations were taken at 10 weeks after sowing. When grown in a monoculture (no competition with IR64 plants), the PWR plants had a lower shoot biomass across N rates than did the MWR and VWR plants. The leaf area and shoot biomass of weedy rice across populations significantly increased with an increase in the N application rate. Each weedy rice population and the IR64 population showed linear responses of the leaf area and shoot biomass to the N rate at all levels of competition. The weedy rice and IR64 plants, when grown without competition, had a similar rate of response in the shoot biomass to the N rate. However, when grown in competition, the response to the added N varied among the weedy rice populations. The MWR plants under competition produced a similar amount of shoot biomass to the IR64 plants per unit addition of N. In contrast, the PWR and VWR populations under competition produced a greater amount of shoot biomass with each additional unit of N, compared to the IR64 population. The results illustrate that N fertilizer management might affect the outcome of weedy rice competition. This information could be incorporated into weedy rice management strategies.