Transition Strategies that Control Perennial Weeds and Build soil

Non-Technical Summary: Perennial weeds are one of the most important problems for adoption, expansion, and sustainability of organic farming. Perennials are a challenge because they produce long-lived underground structures that survive cultivation other control tactics. A survey of organic growers in Ohio showed that perennial weed control was the major limitation to successful transition; some growers were ready to abandon organic methods because of problems with perennial weeds. Perennial weeds require years of persistent effort for effective control, especially in vegetable crops that are not competitive against weeds. Current control methods disturb the soil so much that soil-building goals of organic management are ineffective. Organic farmers need to know how to design transition strategies that allow them to control perennial weeds while building the soil and gaining a financial return during and after transition. We will develop and evaluate transition strategies and outreach information for management of perennial weeds while enhancing soil quality for organic vegetable crop production. Biologically-based and properly timed control efforts, integrated with soil building measures, will provide effective and economical transition strategies that can be readily adopted by organic and transitioning farmers. The research is a response to feedback we have received from organic farmers during our on-farm weed survey as well as during workshops and presentations and telephone conferences. <P> Approach: There will be four basic cropping systems: clean fallow + smother crops, a standard one-crop/year with cultivation, a fabric-culture system designed by a local organic grower, and short-season crops that allow frequent cultivation. Within each system will be three nutrient management options: an untreated control, annual compost applications, and annual compost plus high-calcium lime and other OMRI-approved nutrient additions to achieve nutrient ratios recommended by biodynamic farmers. These treatments will be imposed in an alfalfa/grass hay field, which represents a typical starting point for transition to organic vegetables. This will allow us to evaluate a wide range of strategies that incorporate different mechanical, cultural, and natural-product weed management options together with different nutrient management levels. Performance of these strategies will be evaluated using biological indicators (soil quality, weed suppression) and economic returns during transition, and during the first vegetable crop season after transition. The combination of weed management with nutrient management options will allow us to explore weed/soil interactions that are of great interest to organic farmers. We will work with cooperating farmers to study how perennial weed patches respond to grower management practices. Our rationale is that understanding the behavior of perennial weed populations in response to variations in farm field conditions, soil quality indicators, and farmer management decisions will help us design farm-relevant transition strategies that are more effective in perennial weed suppression. We will focus on the most important perennial weeds identified by farmer cooperators; these are Canada thistle, quackgrass, yellow nutsedge, and field bindweed. In fields that have been managed as pasture or reduced-tillage corn/soybean rotations, it is fairly easy to discern discrete patches of these perennials, due to their interconnected underground vegetative connections. These species also occur in patchy distributions along field edges, from which they spread into otherwise well managed crop fields. Farmers will choose fields that have known perennial weed infestations and patches will be selected to monitor and map changes in these patches and in soil quality indicators; data will also be collected on all inputs and management operations in the fields of interest. Outreach activities will be developed through informal learning communities that have self-organized among organic farmers in Ohio. We will integrate relevant foundational biology and ecology into this network and to bring to it increased scientific rigor to evaluate results from participatory experiments that will be conducted under the domain of this proposal.