Effect of Agricultural Practices on Weed Community Dynamics

Menalled, F. and K.L. Gross

Presented at the All Scientist Meeting (1999-07-20 to 1999-07-21 )

The development of alternative weed management strategies requires a clear understanding of the mechanisms conditioning the establishment, growth and reproduction of invasive plants. This study evaluates the effect of common agricultural practices on weed community dynamics at the KBS LTER site. Specifically, it addresses the following questions: 1) what is the relationship between weed community composition and habitat stability?, 2) do different agricultural practices favor the establishment of certain life-history groups?, 3) is weed community composition determined by the presence of a given crop, the agricultural practice employed or a combination of both factors? Aboveground weed biomass by species was sampled each year (1993-98) at the peak of their occurrence at treatments 1, 2, 3, and 4 using five 1 m2 quadrat (0.5 m x 2.0 m) in each treatment and block combination. All plants rooted in the quadrat were clipped, separated by species, dried to constant weight, and weighed.More species per sample plot were sampled in treatment 3 and 4 (low chemical inputs) than in treatment 1 and 2 (conventional chemical inputs). A multivariate ordination analysis indicated that chemical input is a main factor conditioning weed community characteristics (Fig. 1). Spearman correlation coefficients showed that the number and biomass of perennial species were negatively associated with chemical inputs. Evaluation of Euclidean distances among sample sites suggested that year to year variation in weed communities were larger in conventional treatments than in low-input ones. A correlation analysis between site variables such as soil characteristics, crop yield and seed bank composition will be performed to explore mechanisms responsible for weed community variations as a function of agricultural practices.

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