Abstract: The occurrence and development of weeds in farmland under rice-wheat rotation system andtheir effects on the nutrient balance were studied during 1980—1985.A rice-wheat rotation systemcreated a better condition for propagation of weeds.The biomass of weeds was closely related tothe amount of inorganic nitrogen applied to the soils.The amounts of N,P and K absorbed bythe weeds from soils were 13.1—26.3kg/ha,1.1—2.9kg/ha and 9.1—31.8kg/ha respectively,corresponding to 57—112%,38—81% and 55—230% of the amounts of N,P and K absorbed bywheats,respectively.On the basis of the study some measures for controling weeds were proposed.

Key words: Riparian forest buffers, Riparian, Ecosystem management