Alternative cropping systems alter residual weed community composition
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Weed community composition was assessed in 1994 through 2000 in the Alternative Cropping System Project at Scott, SK. Weeds were counted during July after in-crop management practices had been used. The weed community was composed of 67 species. The nine arable cropping systems in the project were compared in terms of weed frequency, density, and diversity. Changes in weed community composition over time are displayed as a principal response curve (PRC). This method compares the weed community in the cropping systems to a reference system. PRCs are based on redundancy analysis, a constrained form of principal components analysis. Weed densities are constrained to be linear combinations of the interaction of system and year. Seven years and initial spatial variation (4 replicates and 36 sub-plots) are removed as covariables. The PRC analysis identified problematic weed species associated with the cropping systems after six years. Green foxtail, lamb’s-quarters and stinkweed were abundant in the three organic input systems. Wild oats, shepherd’s-purse and narrow-leaved hawk’s-beard were abundant in the reduced input systems. The three organic systems appear to have reached equilibrium after a three-year transition period. The problematic weed species in the reduced systems still appear to be increasing after six years.
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