A Study On Occurance Rule Of Weed Community And Chemical Control In Transplanted Rape Fields After Rice

Transplanted rape after rice is main planting pattern of rape in the lower reaches of Yangtze River. In recent years, grass weeds were dominant in transplanted rape fields after rice, and broadleaf weeds gradually increased. Rape production was endangered by those weeds. Ethametsul-furon was preferred herbicide that could effectively control grass and broadleaf weeds. But residues of ethametsul-furon in soil frequently harmed succeeding crops (eg. rice) due to its slow degradation. In this paper, we first studied occurrence law of weeds in different cultivation-system rape fields and competition of weeds with transplanted rape after rice, then control effect of Youzhuang 21% SC to weeds in rape fields and its security to succeeding rice. The results were as follows:Structure and magnitude of weed communities were completely different in transplanted rape fields after rice, maize and cotton. In transplanted rape fields after rice, hydrophilous weed Alopecurus japonicus was the dominant species, and there were also lots of mesophytic weeds , such as Vicia sativa and Capsella bursa-pastoris. In transplanted rape fields after maize and cotton, mesophytic and xeromorphic weeds dominated in weed communities. Weed magnitude was much less in transplanted rape fields after maize and cotton than that in transplanted rape fields after rice. Weeds had a emergence peak and a density peak before winter in transplanted rape fields. In spring, a few weeds emergenced, and weed density increased slightly in transplanted rape fields after maize and cotton. But weed density increased sharply in transplanted rape fields after rice because of a great deal of grass-weed tillers in spring.Weed biomass increased very slowly before March, but increased sharply after the middle of March. Compared with low density rape, high density rape clearly inhibited weed growth. Compared with the control, the numbers of pods, pods dry weight and stalk dry weight decreased 21.7-36.5% in treatments with vast weeds at the rape flowering-poding stage, and branches and 1000-grain weight also decreased at different degrees. But weeds at the early stage of rape and seedling weeds at the late stage of rape little affected rape. The...