REDUCING CYPERUS ROTUNDUS TUBER POPULATIONS USING STALE-SEEDBED TECHNIQUES IN RICE-ONION CROPPING SYSTEMS

摘要

Purple nutsedge (Cyperus rotundus L.) infestations are increasing rapidly in rainfed rice-onion systems, causing substantial yield losses. In onion, selective control of this weed with chemicals is difficult to achieve, while handweeding breaks tuber chains which can lead to recruitment of new shoots. Stale seedbed techniques prior to crop sowing offer the opportunity to substantially reduce tuber infestations and decrease the amount of handweeding and other weed control inputs during the cropping season. A long term on-farm experiment was conducted to determine the impact of stale seedbeds applied between rice (Oryza sativa L.) and onion (Allium cepa L.) crops over two cropping cycles (1998 to 2000 wet and dry seasons). Stale seedbeds were achieved either by two harrowings (mechanical) or by a single harrowing followed by glyphosate application (chemical), with a 2-week interval between each operation. The treatments were imposed once before either crop or twice before both crops within a one-year rotation cycle. C. rotundus tubers and emerging shoots were counted and crop yields and costs of all weeding operations were recorded in each cropping season. Mechanical or chemical stale seedbed treatments once or twice in the rotation cycle resulted in tuber and shoot densities that decreased over time by 86 to 90%. Handweeding costs also decreased by 50 to 95% while crop yields and net incomes increased over time. Total net incomes from stale seedbed treatments were $1000 more than income from farmer's practice and $2,500 more than income from unweeded plots. Our study, which related C. rotundus population dynamics with reduction of its tuber and shoot densities over time, can be useful in determining mechanistic models aimed at developing alternative weed management strategies using minimum control inputs.