紫花苜蓿田间杂草危害评价

采用Thomas倒置“W”多点取样点及目测相结合的方法，调查得出鄂尔多斯地区的紫花苜蓿（Medicago sativa）田共有19种杂草分属8科，以禾本科、藜科的杂草危害为主，其次分别是苋科、菊科和紫草科的杂草。头茬刈割后的主要杂草群落为猪毛菜(Salsola collina)+虎尾草(Chloris virgata)+灰绿藜(Chenopodium glaucum)+反枝苋(Amaranthus retrofexus)+稗草(Echinochloa crusgalli)+麦家公(Lithospermum arvense)+狗尾草(Setaria viridis)+苍耳(Xanthium sibiricum)，其中前4种杂草对苜蓿的危害率较高，危害级高达2级。而第2茬刈割后的主要杂草群落却是以虎尾草+猪毛菜+麦家公+灰绿藜+反枝苋+狗尾草为主的群落，前3种杂草的危害级较高。采用模糊数学综合评判法，以“草害程度”为评价指标，综合评价了头茬刈割后不同杂草组分对苜蓿田的危害程度，结果表明，各杂草危害程度由大到小为猪毛菜>稗草>虎尾草>反枝苋>灰绿藜>麦家公>狗尾草>苍耳。综合相对多度、株高、危害率、杂草品质和杂草毛、刺对适口性的影响这5个指标，才能全面、系统地反映出各杂草组分对苜蓿的相对危害性。

Occurrence investigation and influence degree of weeds in alfalfa field

There were 19 species of weeds, belonging to 8 families, in alfalfa fields at Ordos, which was investigated by the method of Thomas ‘invented W’ and visual observation with random sampling of multilateral plots. The resultes indcated that the most harmful weeds were mainly from the family of Gramineae and Chenopodiaceae, followed by Amaranthaceae, Compositae and Boraginaceae. In addition, the main weed communities after the first harvest of alfalfa were Salsola collina+Chloris virgata+Amaranthus retrofexus+Echinochloa crusgalli+Lithospermum arvense+Chenopodium glaucum+Xanthium sibiricum+Setaria viridis. Among them, the hazard level of first four weeds was highest, showing a higher hazard degree on alfalfa than other weeds. However, after the second harvest, C.virgata+S.collina+L.arvense+C.glaucum+A.retrofexus+S.viridis were investigated as the dominant weed communities in alfalfa field. Among them, the hazard level was higher among first three weeds. Moreover, the index “influence of weeds” based on the method of fuzzy synthetic evaluation was established to reflect comprehensively the influence degree of different weed components after the first harvest of alfalfa, that is, S.collina>E.crusgalli>C.virgata>A.retrofexus>C.glaucum>C.glaucum>S.viridis>X.sibiricum. Five indicators, namely, relative abundance, plant height, hazard degree, weed quality and impacts of weed’s hair and thorns on palatability should be integrated to comprehensively and systematically reflect the relative harmfulness of various weed components on alfalfa.