关键词: 稻田, 杂草, 出苗, 群体动态

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