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The goal of the proposed work is to improve on-farm production efficiency and soilborne disease management through effective and value-driven applications of mixed-species green manures in organic vegetable cropping systems. Specifically, the following objectives will be pursued:<OL> <LI>Evaluate the efficacy and value of mixed-species green manures in contrasting cropping systems, using a participatory approach. <LI> Characterize the linkages between microbial community structure and soilborne disease suppression expressed in different organic vegetable systems. <LI>Evaluate novel microbial inoculants to enhance the disease suppressive effects of mixed-species green manures. <LI>Enhance value-added green-manure adoption by organic growers using multi-criterion decision analysis (MCDA).</OL> We hypothesize that the benefits of mixed-species green manures are conferred by substrate-induced shifts in structure and activities of soil microbial communities and such shifts result in the associated soilborne disease suppression we have recently documented . We aim to test this hypothesis in coordinated field research and to assist in the practical application of results through integrated, user-driven outreach activities based on thorough socioeconomic analyses. <P>This project will provide a thorough synthesis of the effects and value of mixed-species green manures in organic vegetable crop production systems. The results of the proposed research and extension program will improve the ability of stakeholders to develop a more effective Organic System Plan as it relates to soil quality and soilborne disease management. <P>Specific products of the proposed research will include: a) transformational research papers describing how green manures alter soil and rhizosphere microbial community structure and the extent to which such substrate-based changes can be used to promote natural biological control; b) innovative extension materials (articles, videoclips, fact sheets) and short courses (tailored for farmers or Extension staff and other professionals) that will provide practical advice regarding the impacts, costs, and benefits of using different green manures (with and without microbial inoculants to enhance efficacy) in various cropping systems; and, c) a comprehensive economic assessment of the aggregate benefits of using green manures and microbial inoculants for soilborne disease control in organic vegetable crops.
Non-Technical Summary: The use of mixed species green manures can provide added value in terms of the benefits conferred to the soil and subsequent cash crops through improved plant health. However, detailed science-based recommendations regarding their value and use in different organic agro-ecosystems have not been formulated. And, the underlying ecological basis for their disease suppressing capacities have not been characterized. The goal of the proposed work is to improve on-farm production efficiency and soilborne disease management through effective and value-driven applications of mixed-species green manures and associated microorganisms that suppress crop diseases in organic vegetable cropping systems. We will achieve this goal by conducting innovative and participatory research and extension programs that address the following questions: i) what are the effects and economic value of using mixed-species green manures in various organic vegetable cropping systems; ii) to what extent can mixed species green manures be used to predictably restructure and manage functionally-important microbial populations (i.e. pathogens and their antagonists) in the root zone of cash crops; and, iii) how can the technical and economic barriers to adoption of the most effective mixed-species green-manures for improved productivity and soilborne disease suppression be effectively over come The results of the proposed research and extension program will improve the ability of stakeholders to develop a more effective Organic System Plan. <P> Approach: Under Objective 1, we propose to evaluate the efficacy and economics of using individual and mixed species green manures containing components previously shown to reduce soilborne disease and/or weed pressure and be of particular interest to growers in each region based on stakeholder input. Based on first year results and additional stakeholder input, the Project Directors will select a subset of treatments to be evaluated at multiple locations, each varying in cropping history, soil type and prevailing soilborne pathogen pressure. Economic analyses of the green manure treatments will include steps to assess their economic profitability to producers, relative to current practices, and to project their value at the market level to society. Under Objective 2, we propose to use a variety of molecular methods to identify and characterize the functionally important pathogen and antagonist populations that are significantly affected by the organic amendments evaluated in the field trails of Objective 1. Specifically, we hypothesize that several groups of bacteria, including those recently discovered in our laboratory, will mediate pathogen suppression in a substrate-dependent fashion. TRFLP-based community profiling and DNA macroarrays analyses will be used to quantify the relative abundance of diverse microbes, and those data will be linked to disease assessments at plant, plot, and field scale using multivariate statistical analyses of data provided by all cooperators. Under Objective 3, we propose to investigate the feasibility of developing microbes into useful inoculants to enhance green manure-induced soilborne disease suppression. Specifically, we will evaluate the use of several bacteria linked to durable soilborne pathogen suppression. Such treatments, by virtue of their novelty, are hypothesized to express new mechanisms of action, thus providing the basis for further innovation in the biopesticide industry. Based on the results of the initial screen and feedback from stakeholders, the four most effective inoculum treatments will be selected for further field testing in year 3. Under Objective 4, we will develop uniquely effective Extension and education deliverables throughthe application of a mental models approach combined with an adaptive management plan based on multi-criterion decision analysis (MCDA) to communicate, promote, and analyze stakeholder involvement in this proposed project. This approach provides a systematic framework from which effective communication of project results and benefits can be conveyed To enhance our effectiveness as a collaborative team, we will create an eOrganic research/outreach group that will allow us to communicate efficiently with each other and with the public through private and public workspaces. The public workspace will be used to communicate with other eOrganic groups and deliver extension programming and materials.