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Title: Elucidating the apparent maize tolerance to weed competition in long-term organically managed systems

Author
item RYAN, MATTHEW - PENN STATE UNIVERSITY
item MORTENSEN, DAVID - PENN STATE UNIVERSITY
item BASTIAANS, LAMMERT - WAGENINGEN UNIVERSITY
item Teasdale, John
item Mirsky, Steven
item CURREN, WILLIAM - PENN STATE UNIVERSITY
item SEIDEL, RITA - RODALE INSTITUTE
item WILSON, D - Rodale Institute
item HEPPERLY, P - Rodale Institute

Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2009
Publication Date: 1/7/2010
Citation: Ryan, M., Mortensen, D., Bastiaans, L., Teasdale, J.R., Mirsky, S.B., Curren, W., Seidel, R., Wilson, D.O., Hepperly, P.R. 2010. Elucidating the apparent maize tolerance to weed competition in long-term organically managed systems. Weed Research. 50(1):25-36.

Interpretive Summary: Organic production guidelines eliminate use of herbicides on organic farms, thus organic crops often have more weeds than conventional crops. Despite higher weed levels, organic crops often produce crop yields equal to conventional methods. An experiment was nested within the long-term Farming Systems Trial at the Rodale Institute, Kutztown, PA, to analyze the mechanisms underlying this apparent crop tolerance to weed competition. Under standard management conditions, all cropping systems produced equivalent maize yields even though weedy plant biomass in the organic treatments was between four- and seven-fold greater than in the conventionally managed corn. Increased yield capacity, evidenced when plots were maintained weed-free, and enhanced crop competitiveness when corn was confronted with similar weed populations were the main reasons of this apparent crop tolerance to weed competition in the organic systems. Simultaneously, the experiment illustrated the poor efficacy of mechanical weed management in the organic systems, which is the main reason organic maize did not outyield conventional maize under standard management conditions. This research will inform farmers and agricultural professionals that weeds may have less impact on organic systems than on conventional systems.

Technical Abstract: In a long-term cropping systems trial comparing organically and conventionally managed systems, organic maize production sustained crop yields equal to conventional methods despite higher weed levels. In 2005 and 2006, an experiment nested within the trial was conducted to analyze the mechanisms underlying this apparent crop tolerance to weed competition. Density of mixed weed species was experimentally manipulated to achieve a broad range of weed infestation levels. Under standard management conditions, all cropping systems produced equivalent maize yields even though weedy plant biomass in the organic treatments was between four- and seven-fold greater than in the conventionally managed maize. Increased yield capacity, evidenced when plots were maintained weed-free, and enhanced crop competitiveness were the main pillars of this apparent crop tolerance to weed competition in the organic systems. Increased soil resource availability and a faster relative crop growth rate in the organic systems likely contributed to these factors, which play an important role in buffering crop fitness during years of less than ideal weed control. Simultaneously, the experiment illustrated the poor efficacy of mechanical weed management in the organic systems, which is the main reason organic maize did not outyield conventional maize under standard management conditions.