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Title: Elevated carbon dioxide alters chemical management of Canada thistle in no-till soybean

item Ziska, Lewis

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2010
Publication Date: 9/1/2010
Citation: Ziska, L.H. 2010. Elevated carbon dioxide alters chemical management of Canada thistle in no-till soybean. Field Crops Research. 119:299-303.

Interpretive Summary: As an environment changes, different plant species may respond differently to that change. For example, as carbon dioxide, the source of carbon for plant growth increases, crops and weeds may respond differently. How they respond may, in turn, have significant implications for chemical control of weeds in agriculture. In this three year study, we grew genetically modified soybean (modified so as to be resistance to glyphosate or round-up, a chemical used to control weeds) with Canada thistle under no-tillage conditions at current and projected levels of carbon dioxide. Soybean responded less to projected carbon dioxide than Canada thistle, and as a consequence, Canada thistle became more competitive with greater losses in soybean yield as carbon dioxide increased. Because this was a no-tillage study, weed control was accomplished using chemicals. Yet, Canada thistle became harder to control chemically at the higher carbon dioxide concentration. This study suggests that: (a) differential responses of weeds and crops may make soybean yields more vulnerable to weedy competition as carbon dioxide increases; and, (b), no tillage practices may be harder to implement if rising carbon dioxide increases herbicide resistance in weeds. The information presented here will be of interest to scientists, pesticide applicators, land managers, and policy makers.

Technical Abstract: Differential responses of crops and weeds to anthropogenic climatic change may alter competition and crop yields. Here we examine the role of current and projected increases in carbon dioxide concentration [CO2], on soybean growth and seed yield with and without competition from Canada thistle (Cirsium arvense, a common perennial weed in no-till farming systems), over a three year period using no-tillage practices. Weed control was implemented by applying herbicide (glyphosate) as a pre-emergent treatment at the beginning of each growing season. Under a weed-free condition, Round-up ready soybean demonstrated a significant response of seed yield and total above-ground biomass to elevated [CO2], but no synergistic effect of no-till over time on the response of biomass or yield to [CO2] was observed. Average above-ground weight of Canada thistle was significantly greater at elevated [CO2] for 2008 and 2009, and establishment of thistle increased as a function of [CO2] over time even with pre-emergent applications of glyphosate. Although the presence of Canada thistle reduced seed yield and biomass of soybean for both CO2 treatments from 2007-2009, the reduction was higher for the elevated [CO2] treatment, and a significant [CO2] x Canada thistle interaction was observed for these parameters. Overall, these are the first data to indicate that perennial weeds associated with no-tillage practices could be a greater impediment to crop yields and harder to control chemically in response to rising levels of atmospheric carbon dioxide.