1a.Objectives (from AD-416)
Determine fundamental ecological processes that contribute to successful weed management on organic farms. Determine the mechanisms driving weed seedbank pool size in organic production systems. Determine traits of agronomic crops that contribute to their capability of competing with weeds.

1b.Approach (from AD-416)
Determine various weed population parameters including seedbank density, seed survival, seedling recruitment, biomass, and seed production on organic farms. Analyze weed population changes from archived soil samples and historic weed data collected at the Rodale Institute Farming Systems Trial. Relate weed population data to important ecological parameters such as soil physical and biological properties, predator populations, landscape vegetation, etc. and determine functional relationships where possible. Conduct detailed studies of mechanisms that enhance crop competitiveness against weeds in crop cultivar evaluations at Penn State and at Rodale Institute.

3.Progress Report

This research conducted in the Weed Ecology Laboratory at The Pennsylvania State University focused on comparing weed-crop competition and community assembly in conventional and organic cropping systems in the Rodale Institute Farming Systems Trial. This long-term experiment was initiated in 1981 providing a unique long-term data set for evaluating weed-crop competition and for quantifying weed population dynamics over an extended period of time. Two manuscripts reporting the results from the weed-crop competition research were recently accepted for publication in Weed Research. The first paper, entitled “Elucidating the apparent maize tolerance to weed competition in long-term organically managed systems”, reports on surprisingly high weed biomass loads in the organically managed crops yet, crop yields were equivalent across methods of management. In other words, the organically managed crops were tolerating much higher levels of weed biomass than expected. We then conducted a detailed and more mechanistic study to provide greater insight into the apparent increase in weed tolerance. A manuscript detailing this work entitled “Weed-crop competition relationships differ between organic and conventional cropping systems” confirms that organically managed crops were more tolerant of equivalent levels of weed biomass. The specific mechanisms underlying this response are not known but we hypothesize that weed competition in organically managed crops is buffered by soils with higher organic matter content and associated biological activity. Another manuscript entitled “Weed seed bank and emergent weed community response to long-term organic and conventional management” reports on weed seed banks in the same organic and conventional management systems and is currently under development. This manuscript includes a novel discussion on the underlying principles of weed community assembly in agroecosystems, and will be submitted to the journal Weed Science in September 2009. New research on reducing tillage in organic cropping systems has begun, and is primarily focused on quantifying multi-tactical weed management strategies for soybean no-till planted into cereal rye cover crops. A book chapter that discusses the effects of soil conservation efforts on weed management efficacy was developed. “Direct and Indirect Impacts of Weed Management Practices on Soil Quality in Soil Management: Building a Stable Base for Agriculture” is currently under review and will be published in the near future. Project monitoring and planning for potential new projects were discussed at meetings on December 19, 2008, and February 27, 2009, at Beltsville, Maryland, and February 6, 2009, at State College, Pennsylvania, as well as informal telephone and email communications.