Studies On The Weeds Occurrence Rules And Control Measures In Different Tillage Methods Wheat Fields Of Sichuan Province

According to Sichuan Yearbook of Agricultural Statistics, Wheat is the second important food crops in Sichuan, with annual wheat planted area of about 178-181 million hm2 and annual production of about 1 million tons, accounting for 10% of total grain output. Sichuan is the one of national advantageous regional of wheat production. The tillage methods have been developed into three methods, including rice straw covering no-tillage cultivation, no-tillage and tillage in recent years in Sichuan Basin. The former tow cultivation methods are conservation tillage measures which can effectively decrease the investment of manpower and materials resources, meanwhile protection paddy environment by recycle of the rice straw. But with the area expansion and years application of conservation tillage methods the weeds become a big problem in wheat production. In order to realize sustainable weeds management we surveyed the weeds species and their population dynamics in the three methods of tillage cultivation and studied on the corresponding control measures.In two years studies inverted W nine point sampling was used in investigations on weed community structure and damage in wheat fields of above mentioned tillage cultivation, and field experiment was applied to raise chemical control methods.Our results showed that above 80 species of 20 families consisting of Gramineae,Compositae, Cruciferae and Caryophyllaceae were recorded in wheat field with the three methods of tillage cultivation. The dominant weed species are Annual Bluegrass,Equal ALopercurus,Common Polypogon,Tender Catchweed Bedstraw,Chickweed, and Japanese Mazus.Siebold Buttercup. and Brassica juncea Czern et Coss, Pennsylvania Bittercress and Common Vetch predominant in the certain regions. Cudweed,Japanese Youngia,Rumex dentatus L,Argy Wormwood,Shepherdspurse,Chinese Bothriospermum,Sandwort, Horseweed, and Veronica didyma Tenore. grew generally with low density.Secondly there were significant differences of damage degree caused by weeds in different methods of tillage cultivations. The more serious damage was caused by weed in tillage field than those in no-tillage with same weed control.The damage degree were 5 in tillage field,3-4 in no-tillage and 1-2 in rice straw covering no-tillage.Thirdly with dominant species changing succession of weed community occurred in wheat field. Three different weed communities in wheat field were found in our investigation namely the community of Annual Bluegrass.-Japanese Mazus.-Tender Catchweed Bedstraw., the community of Common Polypogon.-Tender Catchweed Bedstraw.-Brassica juncea Czern et Coss and the community of Annual Bluegrass.-Common Polypogon.-Pennsylvania Bittercress-Tender Catchweed Bedstraw.The comparison of weed species in wheat field at present with those in 2000 indicated that the original dominant weed showed no sign of losing their advantage while less important weed increased in number. For example the infestation of Annual Bluegrass., Japanese Muzus.Jirassica juncea Czern et Coss, Siebold Buttercup., Common Vetch and Pennsylvania Bittercress became so severe in certain region that it was certain that these weeds have developed into dominant species in community succession. But in 2000 these weed species were only less important weed.Fourthly the site investigation of weed occurrence rules carried on three tillage methods indicated that among three tillage methods no significant difference were found in weed species covering mainly 7 species of 5 families which were described as follows:Common Polypogon., Equal ALopercurus, Chickweed., Japanese Mazus, Siebold Buttercup., Rorippa indica (L.) Hiern.and Pennsylvania Bittercress But weed number was different among the different tillage methods, that is to say, the highest number of weeds were recorded in tillage, less in no-tillage and the lowest in rice straws covering no-tillage. The peaks of weed occurred 2-4 weeks after seeding when the number of weed account for 70-80% throughout growth period of wheat.Fifthly herbicide application techniques for weed control in three tillage methods wheat field. Before seeding of wheat non-selective herbicide could be used to clear wheat fields. Types of herbicides depended on the dominance of weed species.The herbicide such as glyphosate or glufosinate-ammonium can be used in case of Japanese Mazus, paraquat and glufosinate-ammonium in case of Cruciferae (such as Pennsylvania Bittercress or India Rorippa).It was not necessary to control weed during later wheat field management in rice straw covering no-tillage wheat field because the covering rice straw could inhabit weeds growth at rice straw coverage of 5000kg/hm2. For tillage and no-tillage field herbicide must be spray to control weeds. The herbicide selections were determined based on the weed community types. (i) The weeds community of Annual Bluegrass.-Japanese Mazus.-Tender Catchweed Bedstraw. Sigma(Methyl two Metsulfuron sodium salt+safty) could be used to control Annual Bluegrass.,MCPA+fluroxypyr-methyl or fluroxypyr toJapanese Mazus control. (ⅱ)The community of Common Polypogon.-Tender Catchweed Bedstraw.-Brassica juncea Czern et Coss. Clodinafop propargyl could be used to control Gramineae weeds,MCPA(or compounded with other bericide) and fluroxypyr-methyl to broadleaf weeds control, (ⅲ) The community of Annual Bluegrass.-Common Polypogon.-Pennsylvania Bittercress-Tender Catchweed Bedstraw.. Sigma(Methyl two Metsulfuron sodium salt+safty) could also be used to control Annual Bluegrass.,harry (MCPA+carfentrazone-ethyl) and Express (tribenuron-methyl) to broadleaf weeds control. Weed control was important to get higher crop yield increasing wheat yields by about 10% in our research. The effects of herbicides on weeds stems and leaves were strongly influenced by stems and leaves sensitivity and herbicide controlling spectrum.