Unearthing the Scent of Soil Health: A Validation of Smell through Odorant VOCs for Farmer Assessment

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Unearthing the Scent of Soil Health: A Validation of Smell through Odorant VOCs for Farmer Assessment

Farmers routinely perceive soil smell in daily field activities. Soils emit a diversity of odorant volatile organic compounds (VOCs), many hypothesized to be relevant to soil health processes. For example, an “earthy” aroma is associated with soil microbial activity, whereas “metallic” smells are associated with compaction. Farmers looking to implement soil health-promoting practices often face barriers to soil health testing. An alternative or complementary approach is farmer-based  empirical assessment. While quantification of complex sensory profiles is challenging, sensory assessment panels are routinely used to assess air quality in regulatory industries, validation of smell as a soil health indicator (SHI) would enable a breakthrough in farmer assessment of soil health. 

Profiling the VOC emissions responsible for soil smell presents an opportunity to validate smell as an SHI. To achieve this, we ask two questions: First, is soil VOC emission related to soil smell? Second, can soil smell traits be validated as a SHI for farmer-driven soil health assessments? Using a 2x3 factorial design that tests the effect of soil type and management diversification, our objectives are to i) establish a semi- quantitative smell profiles from farmer-based smell assessment panels, i) establish VOC emission profiles for smell profiles, then iii) relate smell profiles and constituent VOC emissions to established USDA NRCS SHIs to validate soil smell as a SHI. 

Through collaboration across soil science, sensory science, and chemical ecology, we will profile VOC emissions and conduct farmer-based smell assessment to characterize smell profiles of soils from a range of management practices (e.g. extended crop rotation, livestock integration) for each of two major soil orders of the North Central US. Analysis of the relationships between smell profiles, VOC emission profiles, and SHIs will be conducted to validate smell as an SHI, resulting in a framework to interpret smell as a SHI. This project aims to increase farmer use of soil health testing through producing 1) the knowledge to interpret soil smell as an SHI and 2) an accessible evidence-based on farm tool to support traditional soil health testing during management decisions. In order to disseminate our findings, results will be published in a peer reviewed publication, a popular press article, a webinar, and through several field days followed by a survey to assess project impact on farmer knowledge, skills, attitudes, and awareness towards SHI use and implementation.

Learning outcomes: This research project will generate knowledge on how the smell of soil produced by VOC emissions can be empirically interpreted as an indicator of soil health. By incorporating farmers into the planning and experimental phase of this project, then directly engaging a broader community of farmers through outreach, we anticipate knowledge gained to undergo both formal (popular science article, webinar, field days) and informal (word of mouth) transfer into the regional farmer community.  

Action outcomes:  The action outcome of this research project is to increase farmer use of soil health testing in the north central region. Since soil smell is rapid and inexpensive, we expect that the results of this project will increase farmer use of soil testing, which will improve long term soil health outcomes as farmers will be better equipped to make optimal management decisions. Once validated, smell can be interpreted as a low-cost and rapid supplement to quantitative as lab-based metrics. We expect sustainably minded farmers to implement soil smell as a soil health assessment tool to supplement traditional soil health testing. For example, rather than spending additional funds on tests for biological soil health, which are highly variable, not well calibrated to agroecological outcomes, and expensive, farmers can infer information from soil smell in conjunction with traditional fertility tests to make management decisions.