Compact, Efficient and Economic Soil Steam Disinfestation

The U.S. strawberry crop centered on 40,000 acres in California supplies 30% of the worlds strawberries, a marvel of American agricultural productivity. It is also emblematic of fumigation-supported high U.S. agricultural productivity, achieving soil sterilization of soil-borne pests necessary for high yield by using as much as 400 pounds per acre (at an average cost of $3500/acre) of ozone-depleting greenhouse gas methyl bromide. Although methyl bromide use is being phased out, California strawberries and some other crops are currently operating under critical use exemptions. A viable alternative for soil fumigation is steam, which is known to be highly effective and environmentally safe. However, steam has not been embraced for outdoor applications due to multiple disadvantages including size and capital cost of equipment, slow steam rates and operating costs, water quality requirements, and low fuel efficiencies. Mobile steam applicators, such as the steam rake and the steam blade have been deployed, both being pulled through the soil either by a winch or by a self-propelled unit containing a boiler to produce steam. Typical treatment rates of only around 0.5 acres per day, and costs notably above methyl bromide. The drawbacks to this method again are size, weight, speed and cost. Precision Combustion, Inc. (PCI) supported by the University of California Davis and University of Connecticut proposes to develop a compact direct-fire and high-heat-rate steam generator that can be configured into a cost-effective soil steam sterilization system for agricultural use. PCIs compact, high efficiency steam generator will enable the use of steam on a large and economic scale, providing an improved means of protecting agricultural production systems from diseases and pests. We estimate that costs will be at or below that of methyl bromide, and test results have shown that strawberry yield can be increased by as much as 15%. In Phase I, we will develop the technology to run on farm-available fuels, propane or natural gas,, using available field water, and create engineering solutions to enable the steam generators use on mobile agriculture equipment. We will develop designs resolving the trade-offs between steam generation rates, soil application rates, and support equipment requirements. In addition to significant weight savings and significantly higher heat rates, advantages of the PCI approach includes over 95% fuel energy efficiency, and the use of untreated well water. If successful, we anticipate being able to effectively treat acreage on a costs competitive basis with methyl bromide applications, and potentially with increased yield. Phase I success will lead to a Phase II field trial with strawberries. Success in the field trial with favorable economics could lead to rapid deployment of the technology, including for application with other high-valued crops. The use of steam rather than pesticides and chemical fumigants addresses NIFA / USDA priority research areas as well as Societal Challenge areas of global food security and climate change.