Studies On Community Succession And Chemical Control Of Weeds In The Spring Wheat-rape Rotation Undet Different Tillage Practices

As "rivers source of China’s major rivers " and "ecological source of the eco-systemfunctioning "and water erosion, wind erosion and freeze-thaw erosion ecotone in Qinghai, theimplementation of conservation tillage techniques has far-reaching significance to reducewind and water erosion, mitigate dust hazards and promote the sustainable development ofdry ecological agriculture and the ecological environmental governance of the Qinghai andeven the whole country.In this study, weed survey was conducted by sampling method ofinverted W-pattern to determine the occurrence of farmland weed populations, the communitystructure and succession trends of weed in the area of specific soil background and climaticconditions, and the field trials chemical control methods were proposed in spring wheat andrape farmland in Qinghai.1. There were67weed species belonging to25families in conservation tillage inQinghai. The predominant species were Elsholtzia densa Benth, Galium maborasenseMasamune, Avena fatua Linn, Chenopodium album, Sonchus arvensis Linn., Cephalanoplossetosum (willd.) kitam..The regional predominant weeds species were Polygonum convolvlusL., Lepyrodiclis holosteoides (C. A. Mey.) Fisch. et Mey., Herba Polygoni Avicularis,Setariaviridis (Linn.) Beauv., Hypecoum leptocarpum Hook. F.et Thoms.2. Dominant populations in different parts of the field weed community showedrelatively different.Weed communities in Huangzhong dominated by Galium aparine(L)Vartenerum Rcbb+Elsholtzia densa Benth+Chenopodium album L.+Avena fatua L.+Cephalanoplos setosum(willd)Kitam+Phragmites+Polygonum nepalense Meisn, weedcommunities in Minhe dominated by Setaria viridis+Chenopodium album L.+Polygonumaviculaye L.+Avena fatua L.+Convolvulus arvensis L.+Polygonum oonvolvulus L+Cephalanoplos setosum(willd)Kitam. Communities structure in Pingan were Avena fatua L.+Galium aparine(L)Var tenerum Rcbb+Sonchus brachyotus D C+Cephalanoplossetosum(willd)Kitam+Leymus Hochst+Polygonum oonvolvulus L+Elsholtzia densa Benth+Polygonum aviculaye L.+Euphorbia helioscopia.In Hualong,weeds communities consistedof Lepyrodiclis holosteoides+Galium aparine(L)Var tenerum Rcbb+Avena fatuaL.+Polygonum oonvolvulus L+Sonchus brachyotus D C+Elsholtzia densa Benth, weedscommunities in Datong consisted of Avena fatua L.+Galium aparine(L)Var tenerum Rcbb+ Chenopodium album L.+Cephalanoplos setosum(willd)Kitam+Equisetum arvense l.+Elsholtzia densa Benth,and weeds communities in Gangcha consisted of Elsholtzia densaBenth+Lepyrodiclis holosteoides+Chenopodium album L.+Bromus tectorum+Sonchusbrachyotus D C+Daucus carota.The species richness in conservation tillage of Huangzhongand Datong were48and44species, respectively, and followed in Minhe, only29species inGangcha.3. Emergence of weeds begin in mid to late April, reach emergence peak in early Mayand emergence end in late June in the spring wheat-rape rotation under different tillagepractices.Rainfall is a major factor which affected the emergence of weed in the rain-fedagriculture conservation tillage, which led to the emergence of weeds peak early or delayed.Tillage has greater impact on occurrence of perennial weeds.Density and quantity of annualweeds and perennial weeds were increased significantly with crop no-tillage. Rape strawmulch can effectively suppress the occurrence of Chenopodium album L. and PoJygonumnepalense Meisn..4. Dominant species are annual weeds Elsholtzia densa Benth, Chenopodium album L.Polygonum convolvulus, Galium aparine(L)Var tenerum Rcbb, Hypecoum leptocarpum,PoJygonum nepalense Meisn. and perennial weed Polygonum aviculare L.in the springwheat-rape rotation under traditional farming With the increasing of implementation time ofconservation tillage,annual weeds such as Galium aparine(L)Var tenerum Rcbb,Chenopodium album L. Avena fatua L.were still in an dominant eco-niche in weedcommunities and the communities of perennial weeds such as Elsholtzia densa Benth,Sonchusoleraceus L., Polygonum aviculare L．Sonchus brachyotus D C, Cirsium arvense,Leymus secalinus (Georgi) Tzvel. Equisetum arvense L. gradually succeeded to that of someregion. For seven consecutive years of community succession, Galium aparine(L)Vartenerum Rcbb, Chenopodium album L. Avena fatua, Elsholtzia densa Benth,Sonchusoleraceus L., Sonchus brachyotus D C, Cirsium arvense, Raphanus raphanistrumwere the dominant weed communities and herbicide-resistant weeds population such asElsholtzia densa Benth and Galium aparine(L)Var tenerum Rcbb. Large amount ofseed-produced weeds such as Chenopodium album L. Avena fatua occupied a dominanteco-niche in the competition.Weed seed density is the highest in no-till soil layers and mostweed seeds are concentrated in the topsoil, which indirectly impacted to the dormancy of theweed seeds germinate, once the season into the weeds will lead to the explosive growth ofweeds species and its quantity and species would be significantly higher than plowingfarmland.5. There were little effects for different conservation tillage on controlling effect in post-emergence herbicide. Control efficiency depends mainly determined by the herbicidesensitivity weeds populations and weed spectrum.Pre-sowing soil treatment with herbicides isnot the same degree of mixing with the soil under different tillage patterns, the more adequatemixing with herbicides, the better the weed control effect.Pre-sowing soil treatment with40%Maicaoguang at2700ml a. i./hm2can be used in monocotyledonous and dicotyledonousweeds damage spring wheat field with shallow rotary furrow sowing or shallow rotary flatsowing tillage practices in conservation tillage systems. Post-emergence treatment with7%Maikuojing at1950g a. i./hm2in dicotyledonous weeds damage spring wheat field caneffectively control the weed of conservation tillage fields.The control effect of plant numbersand fresh weight were about90%and the control effect of perennial broadleaf weeds wereabove80%with Youcaoku at1275ml a. i./hm2during3-5leaf stage of Avena fatua L.and2-8leaf stage of dicotyledonous weeds under different tillage systems in rapeseed field. Thecontrol effect were about85%with Longquan at225g a. i./hm2and Bikecao600ml a. i./hm2during6-12leaf stage of Asteraceae weeds such as Sonchus arvensis L., Sonchus brachyotusD C,etc.,and the yield of rapeseed increased above about10%.