Soil Solarization—A Potential Tool for Organic Growers to Manage Weeds and Improve Soil Health By: Jennifer Parke, Carol Mallory-Smith, Maria Dragila, Brian Hill, Nami Wada, and Clara Weidman, Dept. of Crop and Soil Science and Leonard Coop and Kristine Buckland, Dept. of Horticulture Oregon State University, Corvallis
W
eed management and soil health are two of the biggest concerns for organic farmers. There are few options for managing weeds other than hand weeding and mechanical cultivation. Hand weeding contributes to the high cost of labor. Cultivation is fuel-intensive, often involves significant soil disturbance (soil inversion practices such as rotary tilling), and is less effective in controlling weeds within rows. Moreover, soil disturbance is linked to a decline in soil health due to a reduction in soil structure and soil organic matter. Meanwhile, growers identified soil health and weed management as the top two priorities nationwide in the 2016 National Organic Research Agenda. Is there a way to manage weeds in organic crops without harming soil health? Results from Oregon State University soil solarization trials on nursery crops may provide some options.
What is Soil Solarization? Soil solarization is a pre-planting technique in which clear plastic is laid over fallow soil to heat it with solar radiation. The increased soil temperatures can kill certain weed seeds and soilborne plant pathogens. Clear plastic allows sunlight to heat soil directly and to trap heat losses from infrared radiation, evaporation, and convection. Some horticultural poly films designed for covering greenhouses are engineered to prevent condensation and to increase the amount of infrared radiation trapped; these types of plastic result in greater soil heating than regular plastic. While soil solarization has been used successfully in Israel, Spain,
and California, where hot, sunny conditions exist for several months each year, less is known about the effectiveness of this technique in the Pacific Northwest where the “window” for solarization is shorter.
"Soil solarization is a pre-planting technique in which clear plastic is laid over fallow soil to heat it with solar radiation." Oregon State University Soil Solarization Trials With Nursery Crops The Western Sustainable Agriculture Research and Extension (W-SARE) program and the Western Integrated Pest Management (W-IPM) Center funded projects by Oregon State University to determine the effectiveness of soil solarization for managing weeds and soilborne pathogens in tree seedling nurseries in Oregon’s Willamette Valley. Solarization trials were conducted in two commercial nurseries, one in Clackamas County, and one in Yamhill County, during the summers of 2016 and 2017. The plastic used was 1.5-mil anti-condensation, infrared-optimized clear plastic (C-790, Ginegar
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Organic Farmer
December 2018/January 2019