Author
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Smith, Richard |
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GROSS, KATHERINE - MICHIGAN STATE UNIV. |
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Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/28/2007 Publication Date: 10/1/2007 Citation: Smith, R.G., Gross, K.L. 2007. Assembly of weed communities along a crop diversity gradient. Journal of Applied Ecology.44:1046-1056. Interpretive Summary: Increasing the number of different crops grown together in agricultural systems may reduce the need for intensive use of herbicides for weed control. The goal of this study was to assess how, in the absence of fertilizer or herbicides, increasing the number of crops grown in sequence (using crop rotation and cover crops) from one to six crop species over a three-year period impacted the abundance and types of weeds growing in corn, soybean, and winter wheat fields. Results of the study showed that weeds responded more to the type of crop grown in a given year than to the overall number of different crops grown in the cropping-system. Cover crops had a particularly strong suppressive effect on weeds when grown in winter wheat and severely reduced the amount of light reaching the soil surface. The suppressive effect of certain crops, when grown together in diverse rotations, may preclude certain weeds from responding to enhanced soil fertility, and may negate the need for more intensive weed control measures. Technical Abstract: 1. Increasing cropping system diversity is one strategy for reducing reliance on external chemical inputs in agriculture and may have important implications for agroecosystem functions related to the regulation of weed populations and community assembly. However, the impacts of cropping system diversity per se on weed communities have not been formally evaluated in a study comparable to those performed in experimental grasslands, where much of the evidence regarding diversity-ecosystem function has been reported. We performed a field experiment in Michigan USA, in which we manipulated the number of crop species grown in rotation and as winter cover crops over a three year period and in the absence of fertilizer or pesticides, to determine the impact of crop diversity on the abundance, diversity, and composition of the weed community. 2. Crop diversity treatments consisted of three row-crops, corn Zea mays L., soybean Glycine max (L.) Merr., and winter wheat Triticum aestivum L., grown in continuous monoculture and in two and three-year annual rotations with and without cover crops (zero, one, or two legume/small grain species). Weed communities were measured each year at peak biomass and soil resources and light availability were measured over the course of the growing season in the final year of the study. 3. The effects on weed communities of the crop diversity treatments were dependent on rotation phase. In winter wheat weed abundance and diversity (species richness, H’ and D) were lowest in the two highest crop diversity treatments. Across all phases of the rotation, weed community structure was affected more by crop identity than crop diversity per se. 4. In general, the effects on weed communities of crop diversity were due mainly to the presence of cover crops, which had strong effects on soil resource and light levels, particularly in winter wheat. 5. Synthesis and applications. Increasing crop diversity in the absence of external chemical inputs can result in changes in soil resource availability without a concomitant increase in the abundance of weeds or a shift to more-difficult-to-manage weed communities. |
