IMPACT OF AGRONOMIC PRACTICES ON WEED COMMUNITIES - TILLAGE SYSTEMS

Adverse changes in weed communities are a limiting factor for the adop tion of conservation tillage practices. Predictions of an increased as sociation of annual and perennial grasses, perennial dicot weeds, wind -disseminated species, and volunteer crops as weeds, and decreased ass ociation of annual dicot weeds in reduced-tillage systems were tested. Field experiments involving zero-, minimum-, and conventional-tillage systems were conducted in Saskatchewan from 1986 to 1990 at Ituna and Waldron, and from 1986 to 1988 at Tadmore. Weed community composition was analyzed for years 1988 to 1990 by canonical discriminant analysi s. An increased association of perennial and annual grasses with zero tillage did not generally occur. Wind-dispersed species and volunteer crops were associated with reduced tillage and summer annual dicots wi th conventional tillage, but exceptions occurred. Species responded di fferently among sites or within a site over time. Within the time fram e of this research, changes in weed communities were influenced more b y location and year than by tillage systems, indicating fluctuational rather than directional or consistent changes in community composition .