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ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #350832
Title: Weed responses to fallow management in Pacific Northwest dryland cropping systems

Author
item SAN MARTIN, CAROLINA - Oregon State University
item Long, Daniel
item GOURLIE, JENNIFER - Oregon State University
item BARROSO, JUDIT - Oregon State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2018
Publication Date: 9/20/2018
Citation: San Martin, C., Long, D.S., Gourlie, J., Barroso, J. 2018. Weed responses to fallow management in Pacific Northwest dryland cropping systems. PLoS One. 13(9):1-17. https://doi.org/10.1371/journal.pone.0204200.
DOI: https://doi.org/10.1371/journal.pone.0204200

Interpretive Summary: In low rainfall areas of the inland Pacific Northwest, farmland is left unsown for a period of one year to restore the water content of the soil for winter wheat, which is grown once every two years. In the fallow year, frequent tillage is used to eliminate weeds that otherwise would use the soil water intended for the winter wheat. The objective of this study was to determine if one tillage operation is as effective as multiple tillage operations for controlling weeds. Winter wheat was grown in small plots in rotation with either reduced tillage or frequent tillage. Each plot was divided into three areas: a weedy area with no weed control, a general area with chemical weed control, and a weed-free area where weeds were removed by hand. Weed presence was observed in each area over a period of three years. Environmental conditions were found to be the main driver of weed presence but degree of tillage also influenced weed infestation. Grass weed cover (mainly downy brome) was less under reduced tillage than frequent tillage as indicated by higher density and yield of winter wheat. Weeds may have been less competitive under reduced tillage due to higher levels of residues on the soil surface that suppressed weed germination. Reduced tillage can help suppress seedling emergence and growth of grassy weeds in winter wheat in the Pacific Northwest compared to frequent tillage.

Technical Abstract: In the low precipitation region of U.S. Pacific Northwest (PNW), a two-year rotation of winter wheat (WW)/fallow is the most common cropping system. In the fallow year, weeds are frequently managed to maximize soil water storage and potential WW yield. A three-year field study was conducted to evaluate the influence of summer fallow (SF, multiple tillage operations) and reduced tillage fallow (RTF, one tillage operation) on weed species in dryland WW. The experimental design was a randomized complete block with four replications where each phase of the WW/SF and WW/RTF rotations was present every year. Individual plots of WW (30.5 m × 6.1 m) were divided each year into three areas: weedy area with no weed control, general area with chemical weed control, and weed-free area where weeds were removed by hand. Environmental conditions were found to be the main driver of weed presence. However, fallow management also affected weed infestation. The highest impact of RTF on weed management compared to SF was obtained in grass weed cover, which mainly consisted of downy brome (Bromus tectorum L.), and total weed cover. Weeds were less competitive in RTF/WW than SF/WW, as indicated by higher crop density and yield in the WW preceded by a RTF, although differences in yield were not statistically significant. The results of this study suggest that RTF can help suppress seedling emergence and growth of grassy weeds in WW/fallow cropping systems of the PNW compared to SF.