Study On Weed Control In Establishing Alfalfa Fields Seeded In Autumn In South Jiangsu Hilly Area

With the alfalfa industry developing in China, alfalfa was introduced into Jiang-Huai region few years ago and has been spread rapidly. Because of high temperature and excessive rainfall in the region, mass-occurred weeds are really harmful to alfalfa, especially to alfalfa seedlings. The effect of chemical weed control is not steady, and sometimes herbicides cause negative effects to the environment and the quality of alfalfa products. So the problem of weeds is a limiting factor to alfalfa industry development in the region. Based on the historical research, this project selected South Jiangsu Hilly Area as the trial spot. After the diagnosing of weeds occurred round a year in this area, it is found that is a key time to control alfalfa before or after seeding in autumn. There are two aspects in the experiment: agronomy control and chemical control. The agronomy control includes two parts. The first are seed rate and planting mode. The second is companion crops selection, mixture rates and planting modes for weeds control. The chemical control includes herbicides safety to alfalfa seedling, and weeds control in alfalfa field, in order to screen appropriate herbicides and their mixture for alfalfa safety and weeds control. Based on above study, the ecological and the economical effects of techniques have been analyzed. A technical system of weed control in the area has been suggested.There are seven conclusions of the research under the conditions of experiment:1) The weeds occurrence round a year has been investigated, and found out that the establishing period is the pivotal time for alfalfa seeded in autumn in South Jiangsu Hilly Area2) Broadcast sowing at seeding rate of 30kg/ hm2, and drilling at sowing rate of 22.5kg/hm2 are better for weed control.3) Alfalfa(16.7kg/hm2, Durango)- annual ryegrass (25.0 kg/hm2 , Ganxuan NO. 1) broadcast sawing, and alfalfa(16.7kg/hm2, Durango)-triticale(266.7kg/hm2, Zhongxin 830) intercropping with alfalfa raw spacing at 40cm are the two best protection seeding for weed control.4) Eight herbicides are selected out that are safe to alfalfa seedling: They are butralin, trifluralin, imazethapyr, benazolin-enthyl, fluazifop-p-butyl, haloxyfop-R-methyl, quizalofop-p-ethyl, fenoxaprop-p-ethyl.5) The groups of imazethapyr+fluazifop-p-butyl, imazethapyr +haloxyfop-R-methyI, imazethapyr+ quizalofop-p-ethyl are good for weeds control in establishing alfalfa fields seeded in autumn in South Jiangsu Hilly Area, and then gain the mixture rate.6) The competitive relation between alfalfa and weed or other forages in different control techniques has been researched.7) At last, based on the economical analysis, a series suggestion on a technical system of weed control has been submitted.