关键词: 长期施肥, NO₃^--N累积层, 土壤水分布, 氮素回收率

Abstract: By the methods of community ecology,field studies were conducted to evaluate the control effects of three weed management strategies,i.e.,rice-duck farming (RD),manual weeding (MW) and chemical weeding (CW),on the weed communities in paddy fields.The results showed that under rice-duck farming,the weed density in paddy fields decreased significantly,and the control effects on dominant weed species such as Monochoria vaginalis, Cyperus difformis,Sagittaria pygmaea were all above 95%,with an overall effect higher than CW and MW.Under RD,the species richness and Shannon-Wiener diversity indices decreased slightly,while Pielou community evenness indices increased markedly,indicating that the species composition of weed community was greatly improved,and the infestation of former dominant weed species was reduced.The structure of weed communities in paddy fields varied with different weed management strategies,e.g.,under RD,Lindernia procumbens,Cyperus difformis and Fimbristylis miliacea constituted the major weed community,and the Whittaker index was significant higher than that of CW,MW and CK,which indicated that rice-duck farming had a greater effect on the structure of the weed communities.The same conclusion could be drawn from Sorensen's similarity indices and cluster analysis with Sorensen's index as the distance measurement.

Key words: Long-term fertilization, NO₃^--accumulation, Soil moisture distribution, N uptake efficiency