1438694 (VanderGheynst). Soil fumigation with synthetic chemicals including methyl bromide, 1,3-dichloropropene, and chloropicrin, is an effective practice for controlling soil borne pests. However, it also results in accumulation of volatile organic compounds in the atmosphere, contributing to significant levels of air pollution. A promising alternative to toxicant-based soil fumigation involves combining organic soil amendments with soil solarization, in which soil is covered with a transparent plastic film, resulting in passive solar heating of the soil and inactivation of soilborne pathogens. Although combining soil amendments with solarization is very effective, it is not widely used because current practices require treatment during the time in which many crops are produced. The basis of this research is that solarization of amended soil would be utilized more widely if growers could adopt the practice without losing production. It is proposed that two lines of investigation might contribute to greater utilization of solarization: 1) exploration of techniques involving organic matter amendment that increase soil temperature, thereby reducing the time required for solarization and allowing treatment during off-peak production periods; and 2) elucidation of the contributions of microbial communities to organic matter decomposition and soil heating during solarization. Knowledge of the interaction between organic matter decomposition, community structure and organic acid accumulation will allow farmers to make more informed decisions on managing soil organic matter and microbial community amendment for enhanced solarization. Validation experiments will be part of demonstration activities directed towards UC Cooperative Extension educators so that the information gained from the project is disseminated and readily applied to benefit society at large. Also, the results from this research will become part of a 6th grade lesson and activity in the GK-12 program directed by the PI. This program pairs PhD students with 6th grade teachers to develop and deliver STEM curriculum related to renewable energy and environmental sustainability. The lesson and activity will incorporate the effects of short and long-wave radiation on thermal heating and pasteurization of soil. Once tested in classrooms with feedback from teachers, the lesson will be submitted to TeachEngineering.org. Student training will be highly interdisciplinary in engineering and biology.
The overall approach to be pursued involves 1) experiments that examine how organic matter composition and microbial community inoculum can be tailored to facilitate heat generation associated with thermophilic fermentation in soil, 2) an in-depth characterization of microbial community dynamics, and 3) laboratory and field validation experiments. Soil heating studies will be conducted first using laboratory soil columns in temperature-controlled incubators. This will allow investigation conditions under which organic matter soil amendments stimulate aerobic microbial activity, and therefore metabolic heating. To elucidate the role of the microbial community on soil heating, inoculum composition and soil factors will be varied and the resulting community dynamics measured using high-throughput sequencing of extracted DNA. Soil amenability for supporting plant growth will be assessed using phytotoxicity assays. Field studies will be completed to confirm laboratory results and further investigate the effects of organic matter amendment and initial microbial community structure on soil heating and phytotoxicity of solarized soil. This research proposed will improve understanding of microbial activity dynamics and associated soil heating during soil solarization. Preliminary data indicate communities amended with organic matter enhance the rate of biological activity in the soil, however, little is known about the spatial and temporal changes in these communities and how they contribute to organic matter decomposition and production of organic acids that cause phytotoxicity. Next generation high-throughput sequencing will provide fundamental insight into the microbial community dynamics during soil solarization, and the role microbial communities play in soil heating during solarization.
