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Overwintering with plastic silage tarps as a tool to improve the climate resilience of organic vegetable production in British Columbia Kesler, Raelani


Climate change is limiting the use of overwinter cover cropping in organic vegetable production and is driving the need for alternative cover options. Winter soil cover is important in protecting against nutrient leaching and erosion, both of which represent threats to the environment and economic costs to growers. This study investigated impacts of overwinter plastic tarping compared to cover cropping through a mother-daughter field trial in British Columbia. Research was conducted from 2019-2021 on 14 organic practicing vegetable farms, including two mother sites (University of British Columbia Farm and Green Fire Farm) and 12 daughter sites, in three agricultural regions (Lower Fraser Valley, Vancouver Island, and Kootenay Mountains). To determine the relationship between winter cover and crop nutrient sources, three approaches to spring nutrient amendment strategies and a control were trialed at the mother sites: (1) high compost, (2) low compost, (3) compost + fertilizer, and (4) control (no application). Plant available nitrogen (PAN), electrical conductivity (EC), and volumetric water content (VWC) were measured in the spring after tarp removal at all research sites. Additional measurements were taken at the mother sites, including PAN at the time of planting, mid-season, and post-harvest, and crop yield at the time of crop maturity. Spring PAN and EC increased under tarps relative to cover crops in all regions. Impacts to VWC varied between years and likely varies depending on the time of tarp removal. Data from UBC Farm indicate that tarps created lower VWC conditions over the winter until early spring (mid-March) after which time VWC under tarped conditions was higher than soil under cover crops. There were no consistent effects of the winter cover type on crop yields. Nutrient amendment strategies did not meaningfully interact with winter cover type with respect to spring PAN, EC, or VWC. In 2020, nutrient amendment strategy impacted post-harvest PAN at a 0-30 cm depth and crop yield at the mother sites. Results from this study help inform winter cover decisions for small-scale organic growers so that they may decrease the detrimental impacts to soil health from changing precipitation patterns caused by climate change.

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