Organisms produce and use many types of chemical compounds in metabolism, communication, and defense. Soil microorganisms are vigorous producers and consumers of one such type, volatile organic compounds, but our understanding of how the presence of these chemicals in the soil influences nutrient flux, soil health, and plant growth is limited. Soil microbes emit volatile organic compounds at exceedingly low concentrations in hundreds of different varieties, making their comprehensive measurement in soil difficult. Challenges associated with measuring volatile organic compounds quickly and non-invasively have limited our capacity to use the full suite of volatile organic compounds in soil to infer interactions between microbes and plants, and to assess soil health. New approaches and technology for high resolution measurement and monitoring of volatile organic compounds in the soil are needed to better understand how plant-microbe interactions influence carbon and nitrogen dynamics in soil, soil health, and crop production. To address this need, this project aims to: 1) develop a new sensing system to measure volatile organic compounds in soil; and 2) advance understanding of how to ?decode? volatile organic compounds signals of microbial activity. Broader impacts of this research include providing management tools for sustainable agriculture and ecosystem services. The outreach strategy is focused on 1) engaging high school and undergraduate students in research; and 2) designing research and education projects on sensors and data analytics for dissemination through the University of Arizona Biosphere 2 App and on-site activities. Researchers at the University of Arizona (UA) in collaboration with industry researchers at Aerodyne Research, Inc. (ARI) and QuantAQ, Inc. plan to develop a subsurface real-time, in-situ sensing platform to measure volatile organic compound (VOC) signals in the soil. To develop the platform, the project will generate training sets and validate an emerging low-cost VOC sensor against a high-resolution analyzer. Validation activities will use controlled soil columns with increasing degrees of complexity in the soil 'volatilome' (inert matrix, soil, soil and plants), and controlled addition of specific VOCs. To decode VOC signals in soil, the project will: 1) characterize dynamic response of soil VOC composition to wetting in bulk soil and in the rhizosphere; and 2) add VOCs to induce and measure responses in the soil and rhizosphere volatilome. Deliverables of the project include 1) high-resolution VOC soil sampling to generate new understanding of subsurface VOC signals; 2) training sets, and 2) low cost VOC sensor development and validation. The results will contribute to a long-term vision of achieving low-cost, subsurface VOC sensor networks. This award was made through the "Signals in the Soil (SitS)" solicitation, a collaborative partnership between the National Science Foundation and the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA)." This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.