2019 ASHS Annual Conference

Soil is the basis for growing crops, but is also home to weed seeds, pathogens, and insects. These can build up over time to a point that the land is no longer economically viable to farm. Many methods to reduce these soil-based problems have been developed, including fumigation and solarization. Soil fumigation requires the use of chemistries that are toxic and potentially dangerous to users. Additionally, users must be certified and trained to use these chemicals safely. Solarization requires several weeks or even months to be effective. At the turn of the century, steam was used to disinfest soil but fumigation was selected as the preferred method. With restrictions on fumigants and herbicides use under organic production, there is increasing interest in alternative soil-disinfesting methods. We tested soil steaming as a method of reducing weed populations in central Mississippi with a goal of understanding the parameters that impact the time required to reach killing temperatures and optimize its effect on the soil. Steamed sections of soil (500 sq ft for each section) took 1.5-2 hr to reach 180 °F at a depth of 4 in using a steam generator that produces up to 680 lb/hr. The weed population was reduced by more than 95% 5 months after steaming. This would provide enough time for crops to have canopy closure or cover crops to establish before weed seeds repopulated the area. Soils that were tilled after steaming to a depth of 4 to 6 inches developed the same weed density as plots that were not steamed. We also found that soil that is saturated with water or compact was extremely difficult to steam and never reached 180 °F, at a depth of 4 in, within 2 hours. In future work, we will also be evaluating soil steaming on Sclerotium rolfsii, the pathogen that causes Southern Blight on tomatoes and results in large economic loses to tomato farmers in Mississippi. This technology, in its current state, will likely be limited to small farms and high tunnel production. Additionally, a company startup could utilize this technology to improve community public gardens or private gardens of home owners. As improvements are made in steam delivery to the soil, it may be possible to ramp up the size of steaming capacity and the farming operations for which it could be utilized.