Weed Seed Bank Community Of Farmland And Research For Green Weed Management Method

The weed community complex compose of the "potential" weed community-soil weed seedbank and the "real" weed community-aover ground weed vegetation in farmland, and the potential weed community is the primary source of the future weed occurrence and infestations.The study and control of potential weed community play an important role in integrated weed management system (IWM). In the paper quantitative characteristics of the potential weed community of 147 samplings collected in main farmlands of China, and the flora of potential weed communities was studied by associating with environmental conditions. The result showed that a total of 35 families,218 species with a average density of 102851 seeds/m2 were recorded in the seed bank.136 species was recorded in dry fields. Weeds with occurrence frequency higher than 15% were Eleusine indica, Chenopodium album, Capsella bursa-pastoris, Portulaca oleracea, Digitaria sanguinalis, Amaranthus retroflexus, Chenopodium serotinum, Cyperusiria, Cyperus difformis, Setaira viridis, Echinochloa crusgalli, Descuminia sophia, Leptochloa chinensis. Weed seed bank of paddy fields contained 148 weed species. Weeds with occurrence frequency higher than 20% were Cyperus difformis, Alopecurus aequalis, Mazus japonicas, Echinochloa crusgalli, Monochoria vaginalis, Cyperus iria., Lindernia procumbens, Ludwigia prostrate, Leptochloa chinensis, Malachium aquaticum, Lapsana apogonoides, Ammannia baccifera., Ammannia baccifera, Glyceria fluitans, Eleusine indica, Polypogon fugax, Alopecurus japonicas. There were 72 species occurred in both dry lands and paddy fields. Both Shannon-Wiener and Simpson index of paddy fields were higher than dry lands but Pielou evenness was lower. Species diversity index of Northern fields (paddy and dry fields) were lower than Southern fields (paddy and dry fields), but Pielou evenness washigher. Generally all dry lands samples were divided into 6 groups through cluster analysis which were North-East, North China, East China, North cold arid region and tropical/subtropical region. This indicated that there was obvious regional difference in weed seedbank community. Samples were in the lower region similarity in cluster analysis of all paddy fields, which indicated that weed seed bank communities in all of paddy fields were similar under wet environment.Canonical correspondence analysis (CCA) showed that the latitude was the main direct environment causing regional weed area distribution, and indirect reason was average annual temperature and annual precipitation. There was obvious difference in dominant species in different area from geographic regions. From north to south, Chenopodium album, Amaranthus retroflexus, Echinochloa crusgalli are found in north-east China; Chenopodium album, Descuminia sophia, Eleusine indica, Portulaca oleracea were found in northern China; Polypogon fugax, Elsholtzia densa, Hibiscus trionum, Galeopsis bifida Boenn were found in plateau; Ageratum conyzoides, Vernonia patula, Jussiaea linifolia, Sphenoclea zeylanica, Hedyotis corymbosa were found in tropical south China; Echinochloa crusgalli, Cyperus difformis, Mazus japonicas, Cyperus iria, Digitaria sanguinalis, Setaira viridis, Setaira viridis, Portulaca oleracea, Alopecurus aequalis distributed every area in China. Dominants of weed seed banks in potential community were similar to the result of above ground weed survey. Investigation of potential weed community can predict weed occurrence which may be significant to make weed control strategy.The observation of the changes and dynamics of the weed seedbank and the weed control effect under long-term rice-duck farming system (RDFS) were studied from 1999 to 2010. The result showed that density of the whole seedbank decreased 94.01% accumulatively after eleven successive years. Seed reduction of broad-leaf weed and sedge weed was beyond 98%, however, that of grass weed was only 77.09%. Seeds of paddy field weed reduced much more than those of wheat field weed. RDFS made the vertical distribution of weed seed uniform in the soil. Base on the ecological indices, it could be found that the seedbank had gradually evolved to the direction of fewer species, lower density and lower diversity after long-term RDFS. After eleven years of continuous RDFS, the community structure of seedbank had evolved from Lindernia procumbens+Mazus japonicus+Cardamine hirsuta+Alopecurus aequalis to Alopecurus aequalis+Rotala indica+Lindernia procumbens+Cyperus difformis. RDFS made the density of the paddy field weeds decreased annually. Our results provided an important evidence for the positive effect of RDFS on the control of the overground weed community and the underground potential weed community. All in all, RDFS is an effective weed management method based on ecological way.