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Title: Reducing the germinable weed seedbank with soil disturbance and cover crops

Author
item Mirsky, Steven
item Gallandt, Eric - University Of Maine
item Mortensen, David - Pennsylvania State University
item Curran, William - Pennsylvania State University
item Shumway, Durland - Pennsylvania State University

Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2010
Publication Date: 6/1/2010
Citation: Mirsky, S.B., Gallandt, E.R., Mortensen, D.A., Curran, W.S., Shumway, D.L. 2010. Reducing the germinable weed seedbank with soil disturbance and cover crops. Weed Research. 50:341-352.

Interpretive Summary: Ecologically based weed management is more inconsistent than herbicide-based weed management and often results in more weeds reaching maturity and adding seed to the soil seed bank. Low initial weed seedbank densities have been suggested to be critical to the success of ecologically based weed management practices. Therefore, practices that result in rapid depletion of weed seedbanks are important for compensating for these variable weed management practices. In this study, we assess the impact of soil disturbance frequency and cover cropping practices on the germinable fraction of the weed seedbank of common lambsquarters, velvetleaf, and foxtail spp. whose initial seedbank densities were experimentally manipulated by spreading weed seeds of known densities. Seed banks were established at four densities in Pennsylvania and Maine in the fall of 2003 and 2005. Cover crop systems spanned a range of treatments that included greater reliance on tillage on one extreme to a greater reliance on cover cropping to accomplish weed suppression. In general, soil disturbance associated with cover cropping encouraged germination and seedling establishment, thereby reducing the weed seedbank. Of the five cover crop systems studied, the two high soil disturbance systems, the summer fallow and the yellow mustard/buckwheat/winter canola mixture consistently decreased the weed seedbank. Cover crop systems that stimulated weed seed germination through soil disturbance and where weeds were either suppressed by the cover crop or where subsequent tillage controlled emerged weeds resulted in the greatest weed seedbank declines. This research will be useful to weed scientists and growers interested in ecologically based weed management.

Technical Abstract: Ecologically-based weed management relies heavily on a greater integration of cultural and mechanical control tactics. As such, management outcomes are more dependent on the biology of the weed and the interaction between management and weed population size. In this study, we assessed the influence of soil disturbance and cover cropping on the germinable seedbank of common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon theophrasti L.), and foxtail spp. (Setaria spp.) across a range of initial weed seedbank densities. Cover crop systems spanned a range of treatments that included greater reliance on tillage on one extreme to a greater reliance on cover cropping to accomplish weed suppression. In general, soil disturbance associated with cover cropping encouraged germination and seedling establishment, thereby reducing the weed seedbank. Of the five cover crop systems studied, the summer fallow and the yellow mustard (Brassica juncea (L.) Czern.)/buckwheat (Fagopyrum sagittatum Gilib.)/winter canola (Brassica napus L.) mixture consistently decreased the weed seedbank. The magnitude of decline in these high disturbance treatments reached complete depletion of the foxtail germinable seedbank and an 85% and 80% reduction for common lambsquarters and velvetleaf respectively. Both systems included tilling the soil three to four times throughout the growing season. In contrast, treatments including oat/red clover, oat/pea-rye/hairy vetch, and oat or green bean (Phaseolus vulgaris)-rye/hairy vetch involved less soil disturbance and as a result had weed escapes that set seed in one or more site years. Cover crop systems that stimulated weed seed germination and where weeds were either suppressed by the cover crop or where subsequent tillage controlled emerged weeds resulted in the greatest weed seedbank declines.