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Nutrient cycling is an excellent model for testing the sustainability of organic agriculture since it is an inherent component for production and economic success. Careful N management can avoid degradation of environmental quality and can avert environmental impacts on human health while improving social well-being at various spatial scales. <P>The central hypothesis of the proposed research is: The development of innovative plant-soil N testing approaches in the context of researcher-farmer collaborations will result in an improvement in N utilization by organic crops and in the precision of soil nutrient cycling, so that soil quality and C sequestration increase, especially when supported by advance planning for compliance with long-term environmental policies. <P>The specific objectives of this research are: <ul> <LI>Examine the potential for a new N testing approach for organic farmers that more accurately reflects soil N availability based on plant gene expression. <LI> Conduct a landscape survey to assess variables that could serve as new plant-soil testing approaches for diagnostic tools for N management. <LI>Work with farmers and other decision-makers to improve N cycling for organic farms, based on the results of the rhizosphere and landscape studies, and as relevant to recent policies for water quality, C sequestration and reduction of GHG emissions.
<P> Approach: Nutrient management on organic farms is inherently complex, as it relies on the cycling of OM, which is mediated by microbial N transformations. Our long-term goal is to develop a comprehensive set of approaches for nutrient management decisions for organic vegetable production. Developing new plant-soil N testing tools based on plant gene expression, soil bioassays and chemical properties would require substantial effort over the next decade by many stakeholders. This project proposes to explore the potential of this approach, rather than provide end products. Since genetic pathways regulating N uptake are highly conserved across plant species, studies on these N metabolism genes in a model plant such as tomato are highly relevant to other crops. On an organic tomato farm in Yolo Co., CA., the up-regulation of plant nutrient transport and metabolic genes will be studied in response to gross mineralization and nitrification, and organic matter inputs. To validate these responses, and identify novel combinations of nutrient management practices, a landscape survey of organic and conventional farms will be conducted, with site selection guided by GIS analysis. Participatory activities with stakeholders will demonstrate needs, obstacles, and time frames for implementation.