Abstract: Emergence trend and number fluctuation of weeds were observed in fields of wet direct seeded rice in Jiaxing, Zhejiang in 1996-1997. Echinochloa crusgalli, Leptochloa chinensis, Cyperus difformis, Rotala indica, Lindernia procumbens are five main species of weeds, and Mazus japonicus, Ludwigia prostrata, Oenanthe atolonifera and some other weeds are also found in the fields. Numbers of weed species are 25.0%, 18.8%, 56.2% and total numbers of seedling emergence 11.2%, 11.6%, 77.2% for grasses, sedges and broadleaf weeds, respectively. E. crusgalli and L. chinensis are more common in one season rice fields than in other fields, and there are more M. japonicus, L. procumbens, O. atolonifera in early rice fields than in late rice fields. Compared with transplanted rice fields, E. crusgalli, and L. chinensis are more, Eleocharis plantagineiformis, Monochoria vaginalis, O. atolonifera and Ceratophyllum demersum less in the fields of direct seeded rice. Weeds start to emerge in the fields 3 to 4 days after rice is seeded, and emergence peaks appear in 1-3 weeks. For late direct seeded rice fields, the second peak of weed emergence will appear in 6-8 weeks after rice seeded. In the fields of direct seeded rice with tilling cultivation where broadleaf weeds compose the majority of weeds, number of weeds is larger than in non tilling field. The number fluctuation of weeds in direct seeded rice fields showed the same trend as emergence of weed seedlings. In direct seeded rice fields, E. crusgalli, L. chinensis, L. prostrata emerge earliest, followed by R. indica, L. procumbens, M. japonicus and then by C. difformis, O. atolonifera. For E. crusgalli, L. chinensis and other weeds only one peak appears, while for R. indica and L. procumbens the second peak is obvious in the fields of late direct seeded rice.

Key words: emergence, paddy field, population dynamics, weeds

摘要： 1996～1997年在浙江嘉兴调查了湿润直播稻田杂草出苗动态和发生规律，并比较了直播与移栽，早稻、单季晚稻与连作晚稻直播，翻耕与免耕直播间杂草发生差异。湿润直播稻田杂草以稗草、千金子、异型莎草、节节菜、陌上菜为主，其次有通泉草、丁香蓼、水芹。禾本科、莎草科和阔叶杂草种类数分别占25.0%、18.8%和56.2%，出苗数量分别占11.2%、11.6%和77.2%。单季晚稻直播田稗草、千金子发生重于其他直播田，直播田稗草和千金子数量明显高于移栽田。直播田杂草于播种后3～4 d陆续出苗，1～3周达到高峰。连作晚稻直播田播后6～8周出现明显的第二个出苗高峰。以阔叶杂草为绝对优势的翻耕直播田杂草发生重于免耕田。直播田杂草数量自然消长呈现与出苗动态相同的趋势。直播田杂草发生以稗草、千金子、丁香蓼较早，节节菜、陌上菜、通泉草次之，异型莎草和水芹较迟。稗草、千金子及其他几种主要杂草出苗高峰均呈单峰状态，而节节菜、陌上菜在连作晚稻直播田的出苗则为双峰。

关键词: 稻田, 杂草, 出苗, 群体动态