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Title: WEED SEEDBANK AND COMMUNITY SHIFTS IN A LONG-TERM CROPPING SYSTEMS EXPERIMENT

Author
item Davis, Adam
item RENNER, KAREN - MICHIGAN STATE UNIV

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2005
Publication Date: 6/1/2005
Citation: Davis, A.S., Renner, K.A., Gross, K.L. 2005. Weed seedbank and community shifts in a long-term cropping systems experiment. Weed Science. 53:296-306.

Interpretive Summary: Consistent use of a particular weed management strategy over the long-term not only affects weed-crop competition, but can also cause changes in which weeds are dominant in a farmer's field. Our objective was to understand how long-term use of contrasting crop and weed management practices (conventional, no-till, reduced input and organic) affect weed community composition and the relationship between the weed seedbank and emergent weed community at the Kellogg Biological Station Long Term Ecological Research site in Hickory Corners, MI. We found that the weed communities in the conventional and no-till systems remained similar to one another over 12 years, but diverged from the weed communities in the reduced input and organic systems, which were also similar to one another over 12 years. Weed seedbank composition was not a good predictor of the aboveground weed community in the conventional and no-till systems, whereas the seedbank predicted the aboveground community well in the reduced input and organic systems. A striking pattern that held for all four management systems was that weed community diversity was negatively associated with crop yield and biomass. The implications of this result are that 1) preventing new weed species from entering crop fields should be a high priority, and that 2) maintaining healthy, competitive crops is important for suppressing weed communities. This research will have a positive impact on field crop production in the North Central Region by encouraging producers to prioritize high crop vigor and maintenance of low weed community diversity as important components of integrated weed management systems.

Technical Abstract: Characterizing the long-term impact of agricultural management systems on weed communities is an important goal for developing weed management strategies that are effective over time. Feedbacks from weed community shifts influence crop performance and long-term profitability of a cropping system. Weed seedbanks and aboveground biomass abundance and composition were measured within a corn-soybean-wheat crop sequence from 1990 through 2002 at Hickory Corners, MI. Four management systems were compared: conventional (CONV; full rates of N fertilizer and herbicides, moldboard tillage), no till (NT; same as CONV with no primary tillage), reduced input (RI; reduced rates of N fertilizer and herbicides, moldboard tillage, cultivation for weed control, wheat phase underseeded with red clover), and organic (ORG; same as RI but no synthetic inputs). Multivariate ordinations of weed seedbanks showed a clear divergence of the CONV and NT systems from the RI and ORG systems. The CONV and NT seedbanks were dominated by grass weed species (mainly fall panicum and large crabgrass), whereas the RI and ORG systems were dominated by common lambsquarters and common chickweed. Within a single growing season, weed seedbanks in the RI and ORG systems were positively correlated with weed biomass, whereas seedbanks in the CONV and NT system had little predictive value. Weed biomass from 1990 through 2002 showed a strong association of grass weed species with the corn phase of the CONV and NT system, common lambsquarters and redroot pigweed with the corn and soybean phases of the RI and ORG systems, and common ragweed and curly dock with the wheat phase of the RI and ORG systems. In 2002, total weed biomass in the ORG system was 2.8 greater than in RI and 8.4 times greater than in CONV and NT. Diversity of weed biomass was 44% greater for the NT, RI and ORG systems than for the CONV system. Furthermore, weed biomass diversity measures were negatively correlated with soybean yields in RI and ORG, and wheat yields in NT, RI and ORG. It is unclear whether crops were less competitive in the NT, RI and ORG treatments, allowing new weed species to enter the plots, or whether less effective weed management in the NT, RI and ORG treatments resulted in increased species richness, causing reduced crop yields. Mechanistic studies are needed to elucidate the relationship between weed community diversity and crop performance.